BAGHDAD, Iraq —  Militia fighters attacked a provincial headquarters in Karbala, the Shiite holy city south of Baghdad, killing five American soldiers Saturday night, the U.S. military reported.

The military statement said "an illegally armed militia group" attacked the building with grenades, small arms and "indirect fire," which usually means mortars or rockets.

"A meeting was taking place at the time of the attack to ensure the security of Shiite pilgrims participating in the Ashura commemorations," said Brig. Gen. Vincent K. Brooks, deputy commander for Multi-National Division-Baghdad.

Karbala is 80 kilometers (50 miles) south of Baghdad and thousands of Shiite pilgrims are flocking to the city to mark the festivities surround the commemoration of the death of one of Shiite Islam's most sacred saints, Imam Hussein, the grandson of the Prophet Muhammad.

Brooks said the meeting was taking place in the Provincial Joint Coordination Center in the city when the attack occurred. Iraqi officials and security forces as well as U.S. troops were present.

Earlier Saturday, Karbala governor Akeel al-Khazaali had said the U.S. troops raided the provincial headquarters looking for wanted men but left with no prisoners, apparently unable to find their target.

Brooks said that report was incorrect.

"Initial reporting by some media outlets indicated falsely that the attack was conducted by Coalition forces," the military statement said.

"The PJCC is a coordination center where local Iraqi officials, Iraqi security forces and Coalition forces (are) stationed within the center meet to address the security needs of the population," according to Brooks.

Al-Khazaali said the American troops used stun grenades during the raid, causing people living nearby to report the building was under mortar attack. Residents reached by telephone speculated the raiding Americans were after followers of anti-American cleric Muqtada al-Sadr and said helicopters were seen flying over the main al-Sadr headquarters in Karbala well past nightfall.