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.

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.

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