The report said officials reportedly described the defection of the award-winning nuclear expert as "an intelligence coup".

It said Amiri has been extensively debriefed since his defection, and that he helped confirm US intelligence assessments about the Iranian nuclear programme.

Earlier speculation

The Iranian's mysterious disappearance, three days after arriving in Saudi Arabia, sparked speculation that he may have defected to the US.

According to the ABC report, CIA approached Amiri in Iran through an intermediary who made an offer of resettlement on behalf of the US.

At the time Amiri was a researcher at Tehran's Malek Ashtar University working for Iran's Atomic Energy Organisation.

The US has denied any involvement, saying it had no information on him.

In December, Iran accused Saudi Arabia of handing Amiri over to the US.

Quoting from the CIA's declassified annual report to the US congress, the ABC report said: "Iran is keeping open the option to develop nuclear weapons though we do not know whether Tehran eventually will decide to produce nuclear weapons."

Since the late 1990s, the CIA has attempted to recruit Iranian scientists and officials through contacts made with relatives living in the US, according to former intelligence officials.