Update: From the New York Times' Tehran reporter:
It was impossible to confirm first-hand the extent of the new violence in the capital because of draconian new press restrictions on coverage of the post-election mayhem. But the witnesses reached by telephone said the confrontation, outside the national Parliament building, was bloody, with police using live ammunition.
Defying government warnings, the witnesses said that hundreds, if not thousands of protesters, had attempted to gather in front of the parliament on Baharestan Square. They were met with riot police and paramilitary militia, who struck at them with truncheons, tear gas, and guns. One witness said he saw a 19-year-old woman shot in the neck.