Five American soldiers were killed south of Baghdad, including four in a single roadside bombing, the military said Sunday. The blast that killed the four soldiers and wounded four others occurred Saturday during combat operations south of the capital, the military said. The brief statement provided no more details, but the high number of casualties suggested it was likely caused by an explosively formed penetrator, an armor-piercing weapon that the military believes is being smuggled from Iran. Teheran denies the allegation. Another soldier was killed Saturday by small-arms fire during a foot patrol southeast of Baghdad, the military said separately. All the soldiers were assigned to Task Force Marne, which operates in an area with a volatile mix of Sunni and Shi'ite extremists. The deaths raised to at least 3,690 members of the US military have died since the Iraq war started in March 2003, according to an Associated Press count. US and Iraqi forces elsewhere reportedly staged raids in a Shiite stronghold in Baghdad and the holy city of Kufa. A police officer said two civilians were killed and four wounded when the joint forces backed by helicopters stormed into houses in Baghdad's Shi'ite district of Sadr City. The officer, who spoke on condition of anonymity because he wasn't authorized to release the information, also said 16 people were detained. The US military said it was looking into the report.