The American military said Saturday that six militants were killed in an air strike in a Shiite stronghold in northeastern Baghdad, but Iraqi officials and relatives of the victims claimed that 18 civilians died in the attack. The air strike began after American forces came under small-arms fire from a structure near the Husseiniyah area on Baghdad's outskirts just before midnight, the military said, adding that three of the gunmen fled into another building. Attack aircraft dropped a bomb that destroyed that house, setting off at least seven secondary explosions believed caused by explosives and munitions stored inside the building, according to the military statement. Iraqi police inspected the site and reported six militants killed and five wounded, it said. The military account contradicted reports from Iraqi police and hospital officials, who said 18 civilians had been killed and 21 wounded in a 2 a.m. attack in Husseiniyah, an area in which Shiite militias operate openly near the road leading to volatile Diyala province.