The reported disappearance of an Iranian nuclear scientist in Saudi Arabia follows a series of apparent defections and mysterious deaths involving important Iranian figures in recent years that suggest the involvement of U.S. and Israeli intelligence services.

Iranian Foreign Minister Manouchehr Mottaki accused the United States Wednesday of complicity in the disappearance of Shahram Amiri. He vanished in June during a pilgrimage to Mecca, birthplace of the Prophet Mohammed and the most sacred site in the Muslim faith.

Amiri reportedly worked at Malek Ashtar University in Tehran, identified by the United Nations as a nuclear research facility.

It is believed to be linked to the elite Islamic Revolutionary Guard Corps, the Tehran regime's Praetorian Guard, which controls Iran's nuclear program.

Various reports in the Iranian media say Amiri was kidnapped while in Saudi Arabia or defected.

The official Islamic Republic News Agency quoted Mottaki as saying: "We hold Saudi Arabia responsible for Shahram Amiri's situation and consider the United States to be involved in his arrest."

Mottaki reportedly gave a list of several Iranians who have disappeared under suspicious circumstances in recent years to U.N. Secretary-General Ban Ki-moon.

The list included Ali Reza Asghari, a former general in the elite Islamic Revolutionary Guard Corps and a former deputy defense minister. He disappeared in Istanbul in December 2007.

Iran claimed he was kidnapped. But Western sources say he defected and provided the U.S. Central Intelligence Agency with valuable information on Tehran's military as well as its alleged nuclear arms program.

Israel's foreign intelligence service, the Mossad, has intensified its covert war against Iran's nuclear program and, by some accounts, it is targeting Iranian nuclear scientists for assassination as well as sabotaging the Tehran's global procurement network.

Assassination is something the Mossad has carried out in the past to decapitate efforts by Israel's enemies to develop weapons of mass destruction.

In the 1960s the target was German scientists, some of them former Nazis, working with Egypt to build rockets with chemical warheads. Several Germans were assassinated by letter bombs.

In the 1980s and '90s the mission was killing key figures in Saddam Hussein's weapons programs -- at least three high-level scientists -- and bombing European companies supplying components for Baghdad's secret nuclear arms program.

There have also long been suspicions that the Mossad eliminated several of Pakistan's nuclear scientists in the late 1980s and early '90s, at least two by poisoning, in a bid to stop the development of the "Islamic Bomb."

"With cooperation from the United States, Israeli covert operations have focused both on eliminating key assets involved in the nuclear program and the sabotaging of the Iranian nuclear supply chain," says Reva Bhalla, director of analysis with Strategic Forecasting.

The Texas-based private intelligence company has close links to the U.S. security establishment.

American intelligence sources say that several joint Mossad-CIA operations against Iran's nuclear program failed miserably. But at least one senior Iranian official has hinted that they have had some successes.

One of those may have been the mysterious death of Professor Ardeshir Hassanpour, a key figure at the uranium enrichment plant and research center in Isfahan and considered one of Iran's most important scientists.

On Jan. 25, 2007, Iran's state media reported that Hassanpour, 44, had been "suffocated by fumes from a faulty gas fire while he slept."

In fact, he had been found dead six days earlier. There was no explanation for the delay in announcing his demise, possibly indicating that something untoward had occurred.

Bhalla maintains there is "strong intelligence" that Hassanpour was killed by the Mossad.

There are also question marks about the death of at least two other Iranian scientists, apparently caused by poison.

The Israelis and Americans have both carried out industrial sabotage against Iran. Their task has been made infinitely easier because Tehran, unable to buy equipment on the open market due to U.S.-led sanctions, has to rely on the black market, which is easily penetrated.

The Americans have their own clandestine program, which appears to be primarily aimed at inducing Iranian scientists to defect or to spy for the CIA from inside.

According to Arab intelligence sources, the Americans' program has been aided by Sunni Arab regimes in Saudi Arabia and Jordan, which are alarmed by Shiite Iran's expansionist ambitions.