Iran's Revolutionary Guards test fire a missile during military maneuvers at an undisclosed location Sept. 27, 2009. The maneuvers were aimed at

With tensions between Israel and Iran running sky high over the latter's nuclear program, U.S. officials and military analysts are growing increasingly concerned that Israel will launch a multi-phase air and missile attack that could trigger waves of retaliatory missile strikes from Tehran.

Such a shootout could quickly spiral into a regional conflict that would potentially force the U.S. to intervene to protect its interests.

The emerging consensus among current and former U.S. officials and other experts interviewed by NBC News is that that an Israeli attack would be a multi-faceted assault on key Iranian nuclear installations, involving strikes by both warplanes and missiles. It could also include targeted attacks by Israeli special operations forces and possibly even the use of massive explosives-laden drones, they say.

The Iranian response to such an attack is uncertain, but many experts and officials believe it is likely to include retaliatory missile strikes. Iran has more missiles in its arsenal than Israel, according to some estimates, and has the capability of striking targets in most Israeli population centers.

"I think that it would strike Iran as a reasonable response, an eye for an eye," said Christopher J Ferrero, a professor of diplomacy at Seton Hall University in New Jersey and an expert on Middle East missile forces.

Israel possesses advanced anti-missile defenses, but those systems could be overwhelmed if Tehran launched large numbers of missiles, as Ferrero expects.

Reuters

The Center for Strategic and International Studies outlines these options for an Israeli strike on Iran. Click the image for the full-size chart.

Given the immense difficulties in carrying out successful air strikes on the four key Iranian installations using its warplanes alone -- as laid out last week by the New York Times, U.S. officials say Israel would be likely to coordinate such airstrikes with waves of missiles. This would greatly increase the chances of penetrating fortifications that Iran has built to protect some of its key installations and overwhelm Iran's air defenses, said the former and current U.S. officials, who spoke on condition of anonymity.

"Two words:  Jericho missiles," said one former White House and Pentagon official, speaking on condition of anonymity, when asked how Israel would attack Iranian targets at great distances. "They are conventionally armed, have a very small CEP (circular error of probability, meaning they are highly accurate) and can be used in conjunction with a strike fighter operation."

Israel has as many as 100 Jericho ballistic missiles – both short- and medium-range – as well as submarine-launched cruise missiles, though the officials say they believe the latter are unlikely to be used. The short-range Jericho I missiles would be of no use in an attack on Iran, because the targets are far beyond its 300-mile range. However, the  medium-range Jericho II's are capable of  hitting targets as far as 900 miles away – or as far east as Tehran. Israel also tested a Jericho III intercontinental ballistic missile in 2008 and Israeli media have reported that it may have deployed one or more of the weapons, which would put all of Iran within reach.

The missiles would most likely be launched from the Hirbat Zekharyah missile range, midway between Israel and the Mediterranean Coast, according to "Critical Mass: the Dangerous Race for Superweapons in a Fragmenting World," by William E. Burrows and Robert Windrem, and various Israeli press reports.

Although designed to be part of Israel's nuclear deterrent force, the Jerichos can be equipped with high explosives as well as nuclear warheads. U.S. officials have said that an Israeli attack, if it happens, would be intended to surgically take out the nuclear facilities, not inflict the mass casualties that would result from a nuclear attack.

Related coverage:
Iran teams with terror group to kill Iran's nuclear scientists, U.S. officials tell NBC
Panetta report fuels concerns that Israel will attack Iran

Iran has no capability to defend against a missile strike, said Ferrero, the expert on Middle East missile arsenals.

"If the Jerichos are accurate enough to get to their targets, they will get to their targets," he said.

What Iran does have is hundreds of Shahab 3 medium range ballistic missiles, according to U.S. estimates. The Shahab 3 also has a range of roughly 900 miles.

Israel, possibly supplemented by U.S. shipborne anti-missile systems – the Aegis Standard Missile-2 -- could intercept and destroy some of the incoming Iranian missiles, said Ferrero. But the numbers favor Iran, he said.

"I believe that (the Iranians) have a sufficient inventory that they could overwhelm those missile defenses and still get enough missiles through to cause damage," he said.

The critical factor may be the number of  missile launchers in Iran's inventory, Ferrero said, because penetrating Israel's defenses would require numerous  missiles, but also enough launchers to be able to fire them off simultaneously. That number is a closely guarded secret, he said.

Additionally, U.S. intelligence estimates say Iran has supplied Hezbollah with more than 40,000 short-range rockets and missiles since 2006. However, U.S. officials are uncertain whether Hezbollah would follow Iranian orders, and risk Israeli retaliation or, if they did, how many they would fire.  The majority of the rockets and missiles are unguided.  Israel and the U.S. have worked on a short-range missile defense system called Iron Dome, but there are concerns that waves of attacks could overwhelm the system.

Also open to question in U.S. and Israeli military circles is whether an Israeli attack would meet its objective: setting back the Iranian nuclear program anywhere from two to five years.

U.S. officials say Israel would be likely to concentrate its attacks on four key Iranian nuclear complexes. Key facilities within those complexes – the Natanz and Fordo centrifuge facilities, both south of Tehran; the Arak research reactor, southwest of Tehran; and a uranium hexafloride production and research facility near the city of Isfahan – are protected by heavy fortifications, they said.

The Jerichos are stored in tunnels in limestone formations around Hirbat Zekharyah and rolled out for firing. They would likely be used as part of a one-two punch, the officials say. The first attack would be carried out by Israeli strike fighters and would be intended to breach the heavily fortified outer ceilings of the facilities. The second (and possibly even third) wave would be missile attacks aimed at destroying the facilities within, the officials said. 

Asked if Jerichos would have the accuracy and the explosive power to take out hardened bunkers or fortifications believed to be protecting Iran's most-sensitive underground nuclear facilities, a current U.S. official replied, "You would be surprised at their accuracy." The official added that the missiles' warheads would contain a special mix of explosives that could penetrate the Iranian defenses.

U.S. officials also say Israel may have learned the location of facilities that fabricate centrifuge components. These, too, could be targeted.

A 2010 book on the possibility of an Israeli attack laid out the difficulties Israel would face if it attempted to use only its strike fighters on those targets.

 "Attacks against the sites at Natanz, Isfahan and Arak alone would stretch Israel's capability and planners might be reluctant to enlarge the raid further," wrote authors Steven Simon and Dana H. Allin, in "The Sixth Crisis – Iran, Israel and the Rumors of War." Simon, then a fellow at the Council on Foreign Relations, now heads the Middle East Desk at the National Security Council.

The biggest problem is the fortification of the two centrifuge facilities. Simon and Allin describe the challenge using aircraft only.

"Natanz is the only one of the … likely targets that is largely underground, sheltered by up to 23 meters (75 feet) of soil and concrete," they wrote. "… Bombs used in a ‘burrowing' mode, however, could penetrate deeply enough to fragment the inner surface of the ceiling structures above the highly fragile centrifuge arrays and even precipitate the collapse of the entire structure."

But for the attack to have high odds of success, they argue, aircraft would have to drop additional bombs into the cavities created by the first bombs. That would require "time on target" -- a luxury that the Israeli jets at the outermost limits of their 1,100-mile range would likely not have. While they estimate the success rate of such a plan at "better than 70 percent," they call it "complicated and highly risky."

Another difficulty for attacking Israeli aircraft would be finding a route to the targets that could be flown covertly or with the tacit approval of Sunni Arab states, who are at least as frightened of an Iranian nuclear capability as the Israelis.

Simon and Allin (and others) have written that there are three "plausible routes" that Israeli warplanes would take to attack Iran: a northern approach, likely along the Syrian-Turkish border; a central path that would take them over Jordan and Iraq; and a southern route that would transit the lower end of Jordan, Saudi Arabia and Kuwait. The southern route is the most likely, U.S. officials suggest, because the Saudis and other Sunni-dominated Gulf states are eager for someone to take out the Iranian threat. They prefer the U.S. do it, but have reportedly shared intelligence on the Iranian program with the Israelis, if only on a limited basis, according to the U.S. officials.

No matter what route the fighter bombers take, they would use what one U.S. official described as "high-low, low-high" flight paths – flying high first to increase fuel efficiency, then low for most of the trip to evade radar, then climbing high again as the bombs are released in what is known as a "flip toss" from as far as 10 miles from the target.

The Israelis would be prepared to lose aircraft if necessary, the officials said.

Although Simon and Allin do not discuss adding a missile component, other experts, including many current and former U.S. officials, believe the Israelis already have made a decision to have them in the attack menu.

Missile attacks would be coordinated with fighter-bomber attacks (presumably, the Israelis' F-16, F-18 and extended-range F-15I Strike Eagle). The missiles would have to be launched so that warheads strike targets following the strike fighter attacks.  Because of the short flight time, minutes rather than hours in the case of the aircraft, the missile launch would almost certainly take place at the last possible moment to ensure the secrecy of the overall attack.

The Israelis are not planning to use their submarine-launched cruise missile force -- "not enough of them," one official said of the subs. (The Israelis have long had nuclear tipped sub-launched cruise missiles as part of their deterrent force.) 

Beyond the strike fighters and the missile force, U.S. officials suggest the Israelis could use two other "weapons" against Iran.

The first is special operations forces that would be secretly inserted into the country. At the least, they could be employed to illuminate aim points for laser-guided bunker-busting bombs. At the most, they could launch their own attacks on facilities, particularly those believed to contain enriched uranium.

The other is a new generation of large drones with wingspans approaching those of a Boeing 777  (almost 200 feet). Costing $30 million each, the Heron drones are capable of remaining airborne for 40 hours at a time and have a range of 4,600 miles. While they can be equipped with surveillance and electronic warfare equipment, some officials call them "strike drones," meaning they could be loaded with explosives and used to attack Iranian targets.

While the initial days of an Israeli-Iranian conflict would probably be bloody, most experts say that the open warfare would be expected to wind down within days or weeks, since neither side has the ability to occupy the other's territory or enough missiles to sustain attacks.

But that would bring with it its own set of problems, as the conflict would be likely to continue on a lower level, involving covert operations and terrorism.

"You could have a very nasty covert war emerge," said Ferrero.

Robert Windrem is a senior investigative producer for NBC News.

Mehdi Marizad / Fars via AP file

A car that was bombed by two assailants on a motorcycle in Tehran on Jan. 11, killing Iranian nuclear scientist Mostafa Ahamdi Roshan, is removed by a mobile crane. The photo was distributed by the semi-official Iranian photo agency Fars.

By Richard Engel and Robert Windrem
NBC News

Updated: 11:14 a.m. ET -- Deadly attacks on Iranian nuclear scientists are being carried out by an Iranian dissident group that is financed, trained and armed by Israel’s secret service, U.S. officials tell NBC News, confirming charges leveled by Iran’s leaders.

The group, the People’s Mujahedin of Iran, has long been designated as a terrorist group by the United States, accused of killing American servicemen and contractors in the 1970s and supporting the takeover of the U.S. Embassy in Tehran before breaking with the Iranian mullahs in 1980.

The attacks, which have killed five Iranian nuclear scientists since 2007 and may have destroyed a missile research and development site, have been carried out in dramatic fashion, with motorcycle-borne assailants often attaching small magnetic bombs to the exterior of the victims’ cars.

U.S. officials, speaking on condition of anonymity, said the Obama administration is aware of the assassination campaign but has no direct involvement.

The Iranians have no doubt who is responsible – Israel and the People’s Mujahedin of Iran, known by various acronyms, including MEK, MKO and PMI.

“The relation is very intricate and close,” said Mohammad Javad Larijani, a senior aide to Ayatollah Ali Khamenei, Iran’s supreme leader, speaking of the MEK and Israel.  “They (Israelis) are paying … the Mujahedin. Some of their (MEK) agents … (are) providing Israel with information.  And they recruit and also manage logistical support.”

Moreover, he said, the Mossad, the Israeli secret service, is training MEK members in Israel on the use of motorcycles and small bombs.  In one case, he said, Mossad agents built a replica of the home of an Iranian nuclear scientist so that the assassins could familiarize themselves with the layout prior to the attack.

Much of what the Iranian government knows of the attacks and the links between Israel and MEK  comes from interrogation of an assassin who failed to carry out an attack in late 2010 and the materials found on him, Larijani said. (Click here to see a video report of the interrogation shown on Iranian televsion.)

The U.S.-educated Larijani, whose two younger brothers run the legislative and judicial branches of the Iranian government, said the Israelis’ rationale is simple. “Israel does not have direct access to our society. Mujahedin, being Iranian and being part of Iranian society, they have … a good number of … places to get into the touch with people. So I think they are working hand-to-hand very close.  And we do have very concrete documents.”

Two senior U.S. officials confirmed for NBC News  the MEK’s role in the assassinations, with one senior official saying, “All your inclinations are correct.” A third official would not confirm or deny the relationship, saying only, “It hasn’t been clearly confirmed yet.”  All the officials denied any U.S. involvement in the assassinations. 

As it has in the past, Israel’s Foreign Ministry declined comment. Said a spokesman, "As long as we can't see all the evidence being claimed by NBC, the Foreign Ministry won't react to every gossip and report being published worldwide."

For its part, the MEK pointed to a statement calling the allegations “absolutely false.” 

Response to article from the National Council of Resistance of Iran

Ali Safavi, a long-time representative of the MEK, underscored the denial after publication of this article,

"There has never been and there is no MEK member in Israel, period," he said. "The MEK has categorically denied any involvement. The idea that Israel is training MEK members on its soil borders on perversity. It is absolutely and completely false."

The sophistication of the attacks supports the Iranian claims that an experienced intelligence service is involved, experts say. 

In the most recent attack, on Jan. 11, 2012, Mostafa Ahamdi Roshan died in a blast in Tehran moments after two assailants on a motorcycle placed a small magnetic bomb on his vehicle. Roshan was a deputy director at the Natanz uranium enrichment facility and was reportedly involved in procurement for the nuclear program, which Iran insists is not a weapons program.

Previous attacks include the assassination of Massoud Ali-Mohammadi, killed by a bomb outside his Tehran home in January 2010, and an explosion in November of that year that took the life of Majid Shahriari and wounded Fereydoun Abbasi-Davani, who is now the head of Iran’s Atomic Energy Organization.

In the case of Roshan, the bomb appears to have been a shaped charge that directed all the explosive power inside the vehicle, killing him and his bodyguard driver but leaving nearby traffic unaffected.

Although Roshan was directly involved in the nuclear program, working at the huge centrifuge facility between Tehran and Qom, Iran’s religious center, at least one other scientist who was killed wasn’t linked to the Iranian nuclear program, according to Larijani.

Speaking of bombing victim Ali-Mohammadi, whom he described as a friend, Larijani told NBC News, “In fact this guy who was assassinated was not involved in the nitty-gritty of the situation.  He was a scientist, a physicist, working on the theoretically parts of nuclear energy, which you can teach it in every university. You can find it in every text.”

“This is an Israeli plot.  A dirty plot,” Larijani added angrily. He also claimed the assassinations are not having an effect on the program and have only made scientists more resolute in carrying out their mission.

Not so, said Ronen Bergman, an Israeli commentator and author of “Israel’s Secret War with Iran” and an upcoming book tentatively titled, “Mossad and the Art of Assassination.”

Bergman said the attacks have three purposes, the most obvious being the removal of high-ranking scientists and their  knowledge. The others:  forcing Iran to increase security for its scientists and facilities and to spur “white defections.” 

He explained the latter this way: “Scientists leaving the project, afraid that they are going to be next on the assassination list, and say, ‘We don't want this.  Indeed, we get good money, we are promoted, we are honored by everybody, but we might get killed.  It isn't worth it.  Maybe we should go back to teach … in a university.’”

There are unconfirmed reports in the Israeli press and elsewhere that Israel and the MEK were involved in a Nov. 12 explosion that destroyed the Iranian missile research and development site at Bin Kaneh, 30 miles outside Tehran.  Among those killed was Maj. Gen. Hassan Moghaddam, director of missile development for the Revolutionary Guard, and a dozen other researchers. So important was Moghaddam that Ayatollah Khamenei attended his funeral. 

Unlike the assassinations, Iran claims the missile site explosion was an accident; the MEK, meanwhile, trumpeted it but denied any involvement. 

Indeed, there may be other covert operations carried out either by Israel acting alone or in concert with others, according to Bergman.

“Two labs caught fire,” said Bergman, enumerating the attacks. “Scientists got blown up or disappeared.  A missile base and the R&D base of the Revolutionary Guard exploded some time ago, with the director of the R&D division of the Revolutionary Guard being killed along with … his soldiers.” 

Bergman added, “So, a long series of … something that was termed by an Israeli (Cabinet) minister … as ‘mysterious mishaps’ happening and rehappening to the project. Then the Iranians claim, ‘This is Israeli Mossad trying to sabotage our attempts to be a nuclear superpower.’”

Dr. Uzi Rabi, director of the Dayan Center at Tel Aviv University, said the supposed accidents could all be part of “psychological warfare” conducted against Iran. “It seems logical. It makes sense,” he said of possible MEK involvement, “and it’s been done before.”

Rabi, who regularly briefs Israel’s parliament, the Knesset, on Iran also said the ultimate goal of the range of covert operations being carried out by Israel is “to damage the politics of survivability … to send a message that could strike fear into the rulers of Iran.”

For the United States, the alleged role of the MEK is particularly troublesome.  In 1997, the State Department designated it a terrorist group, justifying it with an unclassified 40-page summary of the organization’s  activities going back more than 25 years.  The paper, sent to Congress in 1994, was written by Wendy Sherman, now undersecretary of state for political affairs and then an aide to Secretary of State Madeleine Albright.

The report, which was obtained by NBC News, was unsparing in its assessment. “The Mujahedin  (MEK) collaborated with Ayatollah Khomeini to overthrow the former shah of Iran,” it said. “As part of that struggle, they assassinated at least six American citizens, supported the takeover of the U.S. embassy, and opposed the release of the American hostages.”  In each case, the paper noted, “Bombs were the Mujahedin's weapon of choice, which they frequently employed against American targets.”

“In the post-revolutionary political chaos, however, the Mujahedin lost political power to Iran's Islamic clergy. They then applied their dedication to armed struggle and the use of propaganda against the new Iranian government, launching a violent and polemical cycle of attack and reprisal."

Sean Gallup / Getty Images file

Maryam Rajavi, president of the National Council of Resistance of Iran, greets several hundred Iranian expatriates who had gathered to welcome her at Tegel Airport in Berlin, Germany, on March 22, 2010.

U.S. officials have said publicly that the information contained in the report was limited to unclassified material, but that it also drew on classified material in making its determination to add the MEK to the U.S. list of terrorist organizations. 

The MEK and its sister organizations have since the beginning been run by Massoud and Maryam Rajavi, a husband-wife team who have maintained tight control despite assassination threats and internal dissent. Massoud Rajavi, 63, founded the MEK, but since the U.S. invasion of Iraq has taken a backseat to his wife.

The State Department report describes the Rajavis as  “fundamentally undemocratic” and “not a viable alternative to the current government of Iran.”

One reason for that is the MEK’s close relationship with Saddam Hussein, as demonstrated by this 1986 video showing the late Iraqi dictator meeting with Massoud Rajavi. Saddam recruited the MEK in much the same way the Israelis allegedly have, using them to fight Iranian forces during the Iran-Iraq War, a role they took on proudly.  So proudly, they invited NBC News to one of their military camps outside Baghdad in 1991.

“The National Liberation Army (MLA), the military wing of the Mujahedin, conducted raids into Iran during the latter years of the 1980-88 Iran-Iraq War,” according to the State Department report. The NLA's last major offensive reportedly was conducted against Iraqi Kurds in 1991, when it joined Saddam Hussein's brutal repression of the Kurdish rebellion. In addition to occasional acts of sabotage, the Mujahedin are responsible for violent attacks in Iran that victimize civilians.”

“Internally, the Mujahedin run their organization autocratically, suppressing dissent and eschewing tolerance of differing viewpoints,” it said. “Rajavi, who heads the Mojahedin’s political and military wings, has fostered a cult of personality around himself.”

The U.S. suspicion of the MEK doesn’t end there. Law enforcement officials have told NBC News that in 1994, the MEK made a pact with terrorist Ramzi Yousef a year after he masterminded the first attack on the World Trade Center in New York City.  According to the officials, who spoke on condition of anonymity, Yousef built an 11-pound bomb that MEK agents placed inside one of Shia Islam’s greatest shrines in Mashad, Iran, on June 20, 1994.  At least 26 people, mostly women and children, were killed and 200 wounded in the attack.

That connection between Yousef, nephew of 9-11 mastermind Khalid Sheikh Mohammad, and the MEK was first reported in a book, “The New Jackals,” by Simon Reeve. NBC News confirmed that Yousef told U.S. law enforcement that he had worked with the MEK on the bombing.

In recent years, the MEK has said it has renounced violence, but Iranian officials say that is not true, that killings of Iranians continue.  Still, through some deft lobbying, the group has been able to get the United Kingdom and the European Union to remove it from their lists of terrorist groups. 

The alleged involvement of the MEK in the assassinations of Iranian nuclear scientists provides the U.S. with a cloak of deniability regarding the clandestine killings. Because the U.S. has designated the MEK as a terrorist organization, neither military nor intelligence units of the U.S. government, can work with them.  “We cannot deal with them, “ said one senior U.S. official. “We would not deal with them because of the designation.”

Iranian officials initially accused the Israelis and MEK of being behind the attacks, but they have since added the CIA to the list. Three days after the Jan. 11, 2012, bombing in Tehran that killed Roshan, the state news agency IRNA reported that Iran’s Foreign Ministry had sent a diplomatic letter to the U.S. claiming to have “evidence and reliable information” that the CIA provided “guidance, support and planning” to assassins directly involved in the attack.  

U.S. Secretary of State Hillary Clinton  immediately denied any connection to the killings. “I want to categorically deny any United States involvement in any kind of act of violence inside Iran,” Clinton told reporters on the day of the attack.

But at least two GOP presidential candidates have no problem with the targeting of nuclear scientists.  In a November debate, former House Speaker Newt Gingrich endorsed “taking out their scientists,” and former Pennsylvania Sen. Rick Santorum called it, ”a wonderful thing.”

The MEK’s opposition to the Iranian government also has recently earned it both plaudits and support from an odd mix of political bedfellows.

A group of former Cabinet-level officials have joined together to support the MEK’s removal from the official U.S. Foreign Terrorist Organization list, even taking out a full-page ad last year in the New York Times calling for the removal of the MEK from the U.S. terrorist list.  Former Vermont Gov. Howard Dean, former U.S. Attorney General Michael Mukasey, former U.N. Ambassador John Bolton; former Homeland Security Secretary Tom Ridge, former FBI Director Louis Freeh and former Rep. Patrick Kennedy were among those whose signatures were on the ad.

“There’s an extraordinary group of bipartisan or even apolitical leaders, military leaders, diplomats, the United States … the United Kingdom, the European Union, even a U.S. District Court in Washington, said that this group that was put on the foreign terrorist organization watch list in 1997 doesn’t deserve to be there,” Ridge said in November on “The Andrea Mitchell Show” on MSNBC TV.

U.S. politicians also have been pushing the U.S. government to protect the 3,400 MEK members and their families at Camp Ashraf in Iraq, about 35 miles north of Baghdad.  With the departure of U.S. troops, the MEK feared that Iraqi forces, with encouragement from Iran, would attack the camp, leading to a bloodbath. At the last minute, however, agreement was brokered with the United Nations that would permit the MEK members’ departure for resettlement in unspecified democratic countries.  As of this week, there’s been little movement on the planned resettlement.

Jassim Mohammed / AP file

Iranian fighters with the National Liberation Army, the military wing of the MEK, clean armored personnel carriers in 1997 after a field exercise near Camp Ashraf in Iraq.

The Iranians see what’s happening as terrorism and hypocrisy by the United States.  They have forwarded documents and other evidence to the United Nations – and directly to the United States, they say. 

“I think this is very cynical plan.  This is unacceptable,” said Larijani. “This is a bad trend in the world.  Unprecedented.  We should kill scientists … to block a scientific program?  I mean this is disaster!”

Daniel Byman, a professor in the School of Foreign Service at Georgetown University and also a senior fellow with the Saban Center for Middle East Policy at the Brookings Institution, said that if the accounts of the Israeli-MEK assassinations are accurate, the operation borders on terrorism.

“In theory, states cannot be terrorist, but if they hire locals to do assassinations, that would be state sponsorship,” said Byman, author of the recent book, “A High Price: The Triumphs and Failures of Israeli Counterterrorism.” “You could argue that they took action not to terrorize the public, the purpose of terrorism, but only the nuclear community.  An argument could also be made that degrading the program means that you don’t have to take military action and thus, this is a lower level of violence and that really these are military targets, where normally terrorist targets are civilians.”

But ultimately, Byman said, there is a “spectrum of responsibility” and that Israel is ultimately responsible.

Ronen Bergman, while not speaking on behalf of the Israeli government, suggests that there is a justification, citing an oft-repeated but disputed quote in which Iranian President Mahmoud Ahmadinejad’s said that Israel should be wiped off the face of the earth.

“Meir Degan, the chief of Mossad, when he was in office, hung a photograph behind him, behind the chair of the chief of Mossad,” notes the Israeli commentator.  “And in that photograph you see -- an ultra-orthodox Jew -- long beard, standing on his knees with his-- hands up in the air, and two Gestapo soldiers standing -- beside him with guns pointed at him.  One of -- one of them is smiling.

“And Degan used to say to his people and the people coming to visit him from CIA, NSA, et cetera, ‘Look at this guy in the picture. This is my grandfather just seconds before he was killed by the SS,’” Bergman said. “’… We are here to prevent this from happening again.’"

Richard Engel is NBC News' chief foreign correspondent; Robert Windrem is a senior investigative producer.

Most of the officials said it is highly unlikely that the war-weary U.S. would mount a military attack on Iran, instead relying on financial sanctions and diplomatic pressure to squeeze Tehran. 

Jacquelyn Martin / Pool via Getty Images

U.S. Defense Secretary Leon Panetta speaks with reporters Thursday in Brussels, Belgium, after the conclusion of a day of meetings with fellow NATO defense officials.

By Robert Windrem
NBC News

Police raids in Bangkok, Thailand, which netted a suspected Hezbollah operative Thursday and the makings of bomb-making materials Saturday, represent "one of the most credible Israel-focused threats overseas in a long time," said NBC News analyst Roger Cressey, and "very much the real deal" adds NBC News analyst Mike Leiter.

The two analysts referred primarily to the Saturday raid where police confiscated more than 8,800 pounds (4,000 kilograms) of urea fertilizer and several gallons of liquid ammonium nitrate found in a warehouse in Samut Sakhon, on the western outskirts of Bangkok.

Officials in the U.S. and Israel said Hezbollah could have been planning an attack on the Israeli embassy in downtown Bangkok, near various tourist sites, say Cressey and Leiter. Hezbollah, a Shi'ite Islamist group in Lebanon backed by Syria and Iran, is on the U.S. blacklist of foreign terrorist organizations.

The raid caused both the U.S. and Israel to issue public travel warnings urging their citizens to be cautious.

Information that led to the raid was relayed to Thai police by Israeli intelligence. Police detained a Swedish national of Lebanese origin with alleged links to pro-Iranian Hezbollah militants on Thursday. The intelligence indicated a plot could be carried out between between Friday and Sunday.

Cressey said the fear was that Hezbollah was constructing a large bomb that would have caused a devastating blast in an area that many Americans visit.

"There would have been a lot of collateral damage," said Cressey, a former member of the U.S. National Security Council staff.

Moreover, both analysts note they've been told the threat may not be over, that at least one other operative is being sought. Leiter, former director of the U.S. National Counterterrorism Center, says there is a fear about plots against "secondary targets", either tourist or Jewish, in the Thai capital.

As for the rationale for the attack, Cressey said, "All theories make sense. Can't rank order them yet," while Leiter noted, "It's pretty consistent with the increase in tension between Israel and Iran." Iran has vowed revenge for the killings of its nuclear scientists, which it has blamed on Israel and the U.S.

One possibility raised by both is Hezbollah revenge for the Israeli killing on Imad Mugniyah, the Hezbollah leader who died in a car bombing in downtown Damascus nearly four years ago on February 12, 2008.  Mugniyah was responsible for many anti-American and anti-Israeli terrorist attacks, including the bombing of the U.S. embassy in Beirut in 1983, the Marine Barracks bombing in 1983 and the bombing of the Israeli embassy in Buenos Aires in 1992. Hezbollah vowed revenge for that killing but never carried out attacks that it tied to Mugniyah's death.

Background on the incident from the Associated Press:

National police chief Priewpan Damapong told reporters the suspect, named as Atris Hussein, had given police an address where bomb-making material was being kept.

Priewpan said the suspect had maintained that his group had not planned an attack in Thailand but intended to transport the substances to a third country, which he would not name.

Asked about the discovery, Prime Minister Yingluck Shinawatra told reporters: "I have been informed. I would like to ask people not to panic. We are currently in control of the situation."

Thai officials have seemed irritated by travel advisories issued by the U.S. and Israeli governments, followed by several more since Friday. Foreign Minister Surapong Towijakchaikul said diplomats from countries that had issued warnings would meet with him for an explanation on Monday.

Tourism is a big money-earner for Thailand, and ministers are keen not to deter travelers, especially after the hit to tourism from severe flooding in 2011 and political unrest in 2010.

Yingluck also instructed the defense ministry to consult U.S. embassy officials to discuss its terror warning and seek a retraction.

However, an embassy spokesman later said the terror warning to its citizens was valid and the United States had no plan to rescind it.

Defence Minister Yuthasak Sasiprapha told reporters in the northern city of Chiang Mai on Sunday that Thailand was not the target, although officials have also said that areas of Bangkok frequented by Westerners and Israelis could be hit.

Yuthasak said that a second suspect had managed to leave the country.