An Iranian nuclear scientist who vanished more than a year ago mysteriously turned up in Washington saying he had been kidnapped but the United States denied that he was held against his will.

Iran, which is locked in a standoff with the West over its suspected pursuit of nuclear arms, has repeatedly accused the US Central Intelligence Agency (CIA) of abducting Shahram Amiri, who worked for the Islamic Republic’s Atomic Energy Organization.

Amiri, who went missing during a pilgrimage to the Kingdom of Saudi Arabia more than a year ago, appeared at the Iranian interests section of the Pakistani Embassy, which represents Iran because Tehran and the United States have no diplomatic relations.

A man identifying himself as Amiri has variously said in recent videos that he was kidnapped and tortured; that he was studying in the US; and that he had fled US agents and wanted human-rights groups to help him return to Iran.

Amiri was quoted by Iranian state TV as saying “my kidnapping was a disgraceful act for America.” The mystery surrounding him fuelled speculation that he may have had valuable intelligence about the Iranian nuclear program.

In March, ABC News reported that he defected and was helping the CIA. American officials said Amiri had decided to return to Iran of his own volition.

The United States accuses Iran of using its civil nuclear program as a cover to develop weapons. Iran, which has been hit by four rounds of UN Security Council sanctions over the nuclear issue, says its program is to generate power.

Intelligence about the program is at a premium for the US, which fears that a nuclear-armed Iran would threaten its close ally, Israel, as well as oil supplies from the Gulf and friendly nations in Europe.

“My kidnapping was a disgraceful act for America … I was under enormous psychological pressure and supervision of armed agents in the past 14 months,” Amiri, who is in his thirties, was quoted as telling Iran’s state television in a phone interview.

“Amiri has been escorted by American forces to Iran’s interests section in Washington,” Iran’s PressTV said.

Just what happened to Amiri and how he came to be in the US remained unclear.

In June, the US State Department said that the United States had not kidnapped Amiri but did not address whether another country might have abducted the man and turned him over.

Secretary of State Hillary Clinton told reporters: “Mr. Amiri has been in the United States of his own free will and he is free to go.”

She contrasted his situation with that of three American hikers in Iranian custody.

While American officials denied that they were looking to swap Amiri for the three Americans arrested near the Iraq border about a year ago, raising their case in connection with the nuclear scientist suggested that they might be interested in an exchange.

In Tehran, Iranian Foreign Ministry spokesman Ramin Mehmanparast said: “We do not think it is the right thing to discuss swapping Shahram Amiri for three Americans who illegally entered Iranian territory.”

Iran and the United States severed diplomatic relation following the Islamic Revolution of 1979.

Under the umbrella of the Pakistani Embassy, the Iranian interests section, which is staffed by Iranians, provides consular services including information on travel visas.

American interests in Iran are handled by the Swiss Embassy in Tehran.