"In a sign of further escalation of the crisis in Iran, in the last few hours most reformist politicians from Mosharekat [Islamic Participation], and Mojahedin Enqelab, including Khatami’s brother have been detained. Ahmad Zaidabadi, secretary of Advar Org has also been detained. It looks like an all out purge of reformers is underway. There is no doubt a systematic coup is underway. Unconfirmed reports also indicate both Karrubi and Moussavi may be under house arrest."A name which has been associated with coordinating the crackdown is Mojtaba Khamene'i, son of Supreme Leader Ayatollah Ali Khamene'i.
UPDATE: See also this:
"Various reports indicate that many leading reformists, intellectuals, human rights advocates, and members of the opposition Nationlist-Religious groups have been arrested. Al Jazeera TV has reported that Mr. Rafsanjani has resigned from two powerful positions that he has held, namely, the Expediency Council and the Assembly of Experts (both constitutional bodies). Street demonstrations also broke out in many cities, including Tehran, Mashhad (in northeastern Iran) and Baabol (in northern Iran) with some casualties and many arrests."
(Crossposted to American Footprints)