An Iranian nuclear scientist who claims he was abducted by CIA agents last year and taken to the US is on his way back to Tehran, Iran says.
Foreign Ministry officials, who claim they have evidence Shahram Amiri was kidnapped, told state media he had now left the US.
The US state department has insisted he was in the US of his own free will.
In June, Mr Amiri appeared in three videos giving conflicting stories about how he had arrived in the US.
He said in the first that he had been kidnapped by CIA and Saudi agents while on a pilgrimage.
In the second message he said he had gone to the US to improve his education and was living freely in Arizona.
In the third, he claimed to have escaped from US custody.
On Monday evening Mr Amiri arrived at the Iranian Interests Section of the Pakistani embassy in Washington, which handles Iranian affairs in the US capital, and asked to be repatriated.
Since then, he has renewed his allegations that he was kidnapped, giving more details in an interview from the Iranian diplomatic mission with a Danish TV company.
He said he was abducted while on a pilgrimage to Saudi Arabia.
"A white van stopped in front of me... They told me in Farsi that they were part of another group of pilgrims and said 'We are going towards a mosque and we will be happy to take you as well'," he told Atlantic TV.
"When I opened the door to get in and sit down, the person at the back put a gun to my side and said 'Please be quiet, don't make any noise'."
He said he was drugged and woke up in a military plane which took him to "American territory".
He added that he was put under intense psychological pressure to accept millions of dollars and tell US media that he had defected from Iran with sensitive documents and was claiming asylum in the US - a deal he said he refused to accept.
But in the US, unnamed officials and security sources are claiming that Mr Amiri defected and was put into a programme similar to a witness-protection.
Later, he apparently became concerned for family members he had left behind, had a breakdown and decided to return to Iran, US reports claim.
A US official told the BBC: "He provided useful information to the United States. The Iranians now have him. In terms of win-loss, it's not even a close call."
'Free to go'
Iranian media quoted foreign ministry spokesman Ramin Mehmanparast as saying Mr Amiri would travel back to Iran though a "third country".
"With the efforts of the Islamic Republic of Iran and effective co-operation of Pakistan's embassy in Washington, a few minutes ago Shahram Amiri left American soil and is heading back to Iran," Mr Mehmanparast said.
Another foreign ministry spokesman later said the scientist would make a stopover in Qatar. There are no direct flights from the US to Iran.
In June, Iran claimed it had handed evidence to the US that the scientist had been abducted.
The US had repeatedly said it had no information about Mr Amiri.
However, on Tuesday, Secretary of State Hillary Clinton acknowledged publicly for the first time that the scientist was in the US - but she flatly denied allegations of abduction.
"Mr Amiri has been in the United States of his own free will and he is free to go," she said.
Iranian media reports say Mr Amiri worked as a researcher at a university in Tehran, but some reports say he worked for the country's atomic energy organisation and had in-depth knowledge of its controversial nuclear programme.