Iranian authorities in Teh-ran have detained an American-Iranian social scientist as part of a wider investigation into allegations that the US is seeking a "soft revolution" in Iran.

Former colleagues in the US said Kian Tajbakhsh, who has dual nationality, was detained in the past few days. His arrest follows that on May 8 of Haleh Esfan-diari, also American-Iranian, who headed the Middle East programme of Washington's Woodrow Wilson Center.