Iranian scientist Shahram Amiri, who surfaced in Washington after going missing for more than a year was on his way home on Wednesday, vowing to reveal details of his claimed abduction by US spies.

Officials in the Qatari capital Doha said Amiri had arrived there and would be kept off limits from journalists before taking a flight across the Gulf to Iran after midnight (2100 GMT).

Iran's foreign ministry said the nuclear expert would arrive in Tehran at 5:00 am (0030 GMT) on Thursday.

His mysterious disappearance early in June 2009 while on a pilgrimage in Saudi Arabia, followed by conflicting video footages of a man claiming to be Amiri and talking of being abducted, has baffled the world media for months.

Amiri's disappearance also became linked to rising international pressure over Tehran's controversial nuclear programme, which Iran says is for peaceful purposes but many nations led by the United States fear masks a weapons drive.

On Tuesday, Amiri took refuge in Iran's Interests Section office in Washington and gave interviews to Iranian television, claiming he had been abducted and saying he wanted to go home as soon as possible.

US Secretary of State Hillary Clinton said there was nothing to stop him leaving.

"He's free to go. He was free to come. These decisions are his alone to make," she said.

State Department spokesman Philip Crowley echoed that on Wednesday.

"Nobody coerced him to come here and nobody coerced him to leave," he said. "If he wants to talk about his experiences here, that's up to him."

Before jetting out of Washington on Wednesday, Amiri said he had been abducted at gunpoint in Saudi Arabia.

He said he had been approached by besuited Farsi-speaking men in a car in the Saudi city of Medina and offered a ride to the mosque.

"As I opened the door, one of the passengers pulled out a gun and told me to be quiet. They gave me an injection and when I came around I was in a big plane. I was blindfolded. It was likely a military plane," he said.

Amiri said he had been under "intense mental torture" during the past 14 months and vowed to reveal full details of his ordeal when he returns home.

The disappearance of Amiri, who worked in a university linked with the Revolutionary Guards, sparked accusations by Iranian officials that he was kidnapped by the Central Intelligence Agency.

Washington denied the allegations as well as speculation in the US media that Amiri had defected to the United States and was working with the CIA.

The speculation was further compounded when a man claiming to be Amiri was shown in two different video footages on June 7 -- one claiming he was kidnapped by US agents and the other saying he was studying in Tucson, Arizona.

These videos were followed by a third one a few weeks later in which the man said he had escaped from the custody of US spies in Virginia.

US officials consistently denied Amiri's kidnapped but on Tuesday Crowley confirmed that Washington had been in touch with him.

"The United States government has maintained contact with him," he said, adding that Amiri "has been here for some time, I'm not going to specify for how long."

Crowley also refused to comment on whether Amiri had provided Washington with intelligence.

Amir in his interview broadcast Wednesday rejected reports that he had defected to Washington and shared Iranian nuclear secrets with US experts.

He said he had during the months of his abduction been pressured to say "that I have taken refuge in America at my own will and have brought along ... documents to America. I didn't accept that at all."

Amiri further claimed that Israel was planning to keep him in its "secret prisons" in order to force him to talk "and if I did not talk, they would tell the world media I had cooperated with them and publish forged information in my name."

Iranian Foreign Minister Manouchehr Mottaki said Wednesday that Iran will hold fire on whether to consider Amiri "a hero" until it receives his account of claims he was abducted.

Amiri will recount "what has happened over these past two years, and afterwards we will see if he will be considered a hero," Mottaki said in a response to a question from reporters during a visit to Lisbon.