Reports from Baghdad say U.S. forces have launched a helicopter strike on a Shi'ite district in the western part of the Iraqi capital.
Witnesses said Apache helicopters fired on the private militias of radical Shiite cleric Moqtada al-Sadr on Monday, a day after deadly fighting broke out between rioting Shiite demonstrators and coalition forces.
The new clashes erupted after supporters of the Shiite cleric seized control of at least one government building.
The U.S. administrator in Iraqi, Paul Bremer, branded Moqtada al-Sadr an outlaw and vowed to re-establish law and order.
U.S. troops also began a major operation code-named Operation Vigilant Resolve in Fallujah, a Sunni Muslim stronghold where four American civilian contractors were killed and their bodies mutilated by jubilant mobs last week.