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

The US said he was a willing defector who changed his mind and decided to board a plane home from Washington.

Shahram Amiri was embraced by his family - including his tearful seven-year-old son - after arriving in Tehran in the latest spectacle of a puzzling series of events that left Iran and Washington with starkly different accounts.

Mr Amiri flashed a V-for-victory sign as he stepped into the terminal.

Iran portrayed the return of Mr Amiri as a blow to American intelligence services that were desperate for inside information on Iran's nuclear programme.

Iran sought maximum propaganda value - allowing journalists to cover Mr Amiri's return and having a top envoy from Iran's Foreign Ministry on hand to greet him.

Washington described the 32-year-old Mr Amiri as someone who reached out to US officials, but offered few other details.

Speaking to journalists after a flight via Qatar, Mr 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 US.

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

"I was under the harshest mental and physical torture," he 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 officers offered him US$50 million to remain in America.

Mr Amiri gave no further details to back up the claims or shed any new light on his time in the US, 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 US intelligence services," he told reporters.

He sought to downplay his role in Iran's nuclear programme - which Washington and allies fear could be used to create atomic weapons. Iran said it only seeks energy-producing reactors.