An Iranian nuclear scientist claimed Thursday that he suffered extreme mental and physical torture at the hands of U.S. interrogators after disappearing last year, adding to Tehran's allegations he was abducted by American agents.

The U.S. says Shahram Amiri was a willing defector, who changed his mind and decided to board a plane home from Washington.

Amiri was embraced by his family — including his tearful seven-year-old son — after arriving in Tehran.Shahram Amiri, an Iranian nuclear scientist who disappeared a year ago, holds his seven-year-old son Amir Hossein as he arrives at the Imam Khomeini airport just outside Tehran. (Vahid Salemi/Associated Press)

The U.S. government described the 32-year-old Amiri as someone who reached out to American officials but have offered few other details.

Speaking to journalists after a flight via Qatar, Amiri repeated his earlier claims that he was snatched while on a pilgrimage last year in the Saudi holy city of Medina and carried off to the United States.

He claimed he was under intense pressure during the first few months after his alleged kidnapping.

"I was under the harshest mental and physical torture," Amiri said at Tehran's international airport, with his young son sitting on his lap.

He also alleged that Israeli agents were present during the interrogations and that CIA agents offered him $50 million to remain in America. He gave no further details to back up the claims or shed any new light on his time in the U.S. but promised to reveal more later.

"I have some documents proving that I've not been free in the United States and have always been under the control of armed agents of U.S. intelligence services," he told reporters.

Amiri also sought to downplay his role in Iran's nuclear program, which Washington and allies fear could be used to create atomic weapons. Iran says it only seeks energy-producing reactors.

"I am a simple researcher who was working in the university," he said. "I'm not involved in any confidential jobs. I had no classified information."

Last month, Iranian state TV broadcast a video Amiri purportedly made from an internet cafe in Tucson, Ariz., and sent to Iranian intelligence claiming U.S. and Saudi "terror and kidnap teams" snatched him.

In another, professionally produced video, he said he was happily studying for a doctorate in the United States. In a third, shaky piece of video, Amiri claimed to have escaped from U.S. agents in Virginia and insisted the second video was "a complete lie" that the Americans put out.

U.S. officials never acknowledged Amiri was on American soil until Tuesday, hours after he turned up at the Iranian interests section at the Pakistani Embassy in Washington, asking to be sent home.

Secretary of State Hillary Rodham Clinton said Amiri had been in the United States "of his own free will and he is free to go."

U.S. officials would say little about the circumstances of Amiri's defection and what went wrong. But there were suggestions that threats to his family in Iran pushed Amiri to first make the claims he was kidnapped.

Amiri had originally "left his family behind, that was his choice," said a U.S. official who was briefed on the case, speaking on condition of anonymity because the official was not authorized to talk publicly about the case.