A top Iranian former nuclear negotiator Hossein Mousavian has been detained, according to sources in Iran who did not want to be named.
Mousavian was a senior nuclear negotiator in talks with Europe
It is not clear why Mr Mousavian, who has also served as Iran's ambassador to Germany, was arrested.
Eight security officials reportedly took him from his house on Monday.
Hossein Mousavian was deputy to Iran's chief negotiator in talks with Europe on the nuclear issue before President Mahmoud Ahmadinejad came to power.
BBC Tehran correspondent Frances Harrison says he is still close to former President Rafsanjani.
Mr Mousavian has been working in a think tank since the change of government.