The Iranian scientist who American officials say defected to the United States, only to return to Tehran on Thursday, had been an informant for the Central Intelligence Agency inside Iran for several years, providing information about the country's nuclear program, according to US officials.
The scientist, Shahram Amiri, described to American intelligence officers details of how a university in Tehran became the covert headquarters for the country's nuclear efforts, the officials confirmed.
While still in Iran, he was also one of the sources for a much-disputed National Intelligence Estimate on Iran's suspected weapons program, published in 2007, the officials said.
For several years, Amiri provided what one official described as "significant, original" information about secret aspects of his country's nuclear program.
This account by the Americans, some of whom are apparently trying to discredit Amiri's tale of having been kidnapped by the CIA, provides the latest twist in one of strangest tales of the nuclear era.
It also provides the first hint of how the US acquired intelligence from Iranian scientists, besides its previously reported penetrations of Iranian computer systems.
Amiri arrived in Tehran on Thursday repeating his allegation that he had been grabbed in Saudi Arabia by the CIA and Saudi intelligence, and tortured.
American officials, clearly embarrassed that he had left a program that promised him a new identity and benefits of $5 million, said his accusations that he had been kidnapped and drugged were manufactured, and an effort to survive what will almost certainly be a grilling by the Iranian authorities.