The U.S. military in Iraq says four American Marines were killed in clashes with insurgents in Anbar province west of Baghdad late Monday.
A statement said the four were members of the 1st Marine Expeditionary Force and that they were killed while "conducting security and stabilization operations." The statement did not give further details.
The Marines have taken responsibility for a vast region of western Iraq, which includes the restive towns of Fallujah and Ramadi.
Meanwhile, in the southern town of Nassiriya, armed supporters of radical Iraqi Shi'ite Muslim cleric Moqtada al-Sadr clashed with Italian troops, trying to disperse several hundred Shi'ite demonstrators blocking the town's bridges.
Italy's ANSA news agency says 11 Italian soldiers were wounded.
Armed supporters of Moqtada al-Sadr clashed Sunday and Monday with coalition forces in Baghdad. Sunday's fighting left nearly 60 people dead, including one Salvadoran and eight U.S. soldiers.
Monday, the U.S.-led coalition authority revealed that an arrest warrant, signed by an Iraqi judge, was issued several months ago for the radical Shi'ite cleric and at least 30 alleged accomplices in connection with the murder of a rival last year in Najaf.
The cleric was reported holed up in the main Shi'ite mosque in the central city of Kufa, surrounded by armed supporters.
Meanwhile, news reports quote an unnamed senior U.S. official as saying American military commanders are considering contingency plans to send more troops to Iraq if the situation there grows worse.
But the official said no decision has been made to supplement the 134,000 U.S. troops already in Iraq as part of the total 155,000 strong coalition forces.
U.S. officials say the new surge of violence by Shi'ite Muslims represents a challenge to U.S. plans to handover power to Iraqis in less than 90 days.
But President Bush said Monday that June 30 remains the "firm" date for the transfer of power in Iraq - despite the recent violence.
Some information for this report provided by AP, AFP and Reuters.