The CIA has declined to comment on the latest report
An Iranian nuclear scientist who has been missing since June has defected to the US, according to a US media report.
ABC News said Shahram Amiri had been resettled in the US and was helping the CIA in its efforts to block Iran's nuclear programme.
Mr Amiri disappeared in Saudi Arabia while on a Muslim pilgrimage.
Iran accused the US of abducting him but Washington denied any knowledge of the scientist. The CIA has declined to comment on the latest report.
Mr Amiri worked as a researcher at Tehran's Malek Ashtar University, according to Iran's state-run Press TV channel.
However, some reports said he had also been employed by Iran's Atomic Energy Organisation, and had wanted to seek asylum abroad.
The US and its Western allies suspect Iran of secretly developing nuclear weapons - a claim denied by Tehran.
According to ABC, the scientist has been extensively debriefed, and has helped to confirm US intelligence assessments about the Iranian nuclear programme.
His defection was apparently the result of a wider operation, under which the US has been approaching Iranian scientists, sometimes through relatives living in America, to try to persuade them to defect.
By making this defection public, it appears the Americans are putting more psychological pressure on the Iranian authorities, says the BBC's Tehran correspondent Jon Leyne, who is in London.
Iran's nuclear programme is the subject of extensive intelligence work in the West with the aims of gathering information on it, preventing Iran buying equipment for it and, reportedly, sabotaging the programme by selling Iran defective parts on the black market, our correspondent says.
Quite how important Mr Amiri is, or what information he can provide, has not emerged, our correspondent adds.