"Shahram Amiri, Iran's nuclear scientist who had gone to hajj in Saudi Arabia, was handed over by Riyadh to Washington," Ramin Mehmanparast told Mehr, referring to umra, a lesser pilgrimage to Islam's holiest sites.

The spokesman said Amiri was one of 11 Iranian detainees currently held in US jails.

His statement was the first acknowledgement by Tehran that Amiri was a nuclear scientist.

Iranian officials have previously said Amiri went missing in Saudi Arabia soon after he landed there as a pilgrim earlier this year.