Karbala, Iraq ? U.S. combat deaths since the end of major fighting passed the 100 mark Friday after a joint U.S.-Iraqi patrol confronted gunmen outside the headquarters of a Shiite Muslim cleric, triggering clashes in which three Americans and 10 Iraqis were killed, including two Iraqi policemen.

Another American soldier was killed and two were wounded by a roadside bomb near Baghdad, and nine U.S. troops were wounded in a roadside bombing in Mosul.

The four deaths made it the deadliest day for American soldiers in Iraq since Sept. 18, when three soldiers were killed in an ambush. With the latest deaths, the number of U.S. soldiers who have died by hostile fire since President Bush declared an end to major combat May 1 has climbed to 101; the total deaths are 198.

During a visit Friday to U.S. troops in Tikrit, Lt. Gen. Thomas Metz, commander of the Army’s 3rd Corps, told reporters American troops would be in Iraq for another troop rotation or even two.

The bloody battle in the Shiite Muslim holy city of Karbala, about 50 miles southwest of Baghdad, took place over a 12-hour period. It underscores the dangers of trying to disarm militias maintained by Shiite clerics who wield considerable influence in Iraq’s largest religious group. The U.S.-led coalition has banned private militias and is committed to disarming them.

The three Americans who were killed came from the 101st Airborne Division, according to Maj. Mike Escudie of the U.S. Central Command in Tampa, Fla. Seven Americans were wounded, U.S. officials said.

Eight of the Iraqi gunmen died and up to 18 were wounded in the battle, which started about midnight Thursday and continued intermittently until late Friday morning.

Pentagon officials said they were investigating how the shooting began. Iraqis said Americans fired first.

U.S. military spokesman Lt. Col. George Krivo said the trouble began when a joint U.S.-Iraqi patrol found gunmen in front of a mosque after the nighttime curfew. The 9 p.m. curfew was imposed in Karbala this week after clashes between supporters of rival Shiite clerics.

However, gunmen who said they took part in Friday’s fighting said the battle began outside the house of Grand Ayatollah Mahmoud al-Hassani, less than half a mile from the mosque. The house also served as the ayatollah’s headquarters.