BAGHDAD, Iraq — Four U.S. Army soldiers were killed yesterday west of the capital in a province where American troops launched a massive sweep two weeks ago to root out insurgents, the military said.

The soldiers, assigned to the 1st Marine Expeditionary Force, were killed "while conducting security and stability operations" in sprawling Anbar province. The Marines did not say where in Anbar the soldiers were killed. The region, which borders Syria, Jordan and Saudi Arabia, has been a center of insurgent activity.

The deaths brought to at least 1,506 the number of U.S. service members who have died since the United States invaded Iraq in March 2003. At least 1,145 died as a result of hostile action, according to the Defense Department.

A Bulgarian soldier was shot and killed yesterday in central Iraq, becoming Bulgaria's eighth casualty since the start of the war. Bulgaria has a 430-member peacekeeping battalion stationed in the town of Diwaniya.