A female suicide bomber detonated her explosives belt in a crowd of police recruits northeast of Baghdad on Tuesday, killing at least 14 people, police and hospital officials said. The woman donned a black abaya and walked into a crowd of about 200 police recruits at the main gate of the Muqdadiyah police station, said a police officer on the scene. At least 14 people were killed and 20 injured, said an official at Muqdadiyah General Hospital, also on the same condition of anonymity. The death toll was expected to rise. The police recruits had gathered at the station to eagerly await word about whether they were accepted into the police force there, the officer said. Muqdadiyah, a mostly Sunni Muslim city, lies about 90 kilometers northeast of Baghdad. The US military on Tuesday announced the deaths of four US soldiers - three killed by a roadside bomb in Baghdad and another killed in combat in western Anbar province. The three were killed Monday by a roadside bomb and a secondary explosion, while on patrol in a southeastern section of the Iraqi capital, the US military said in a statement. The unit had been conducting raids against militants in the area, and had recently captured five suspects, it said. Another US soldier was killed the same day while conducting combat operations in Iraq's western Anbar province, another statement said. At least 3,285 members of the US military have died since the beginning of the Iraq war in March 2003, according to an Associated Press count. The figure includes seven military civilians. Repeated artillery fire rang out across Baghdad at midday Tuesday, but the target was unclear. Also Tuesday, the US military said it captured more than 150 suspected insurgents in a nearly two-week operation north of Baghdad. Rocket-propelled grenades and launchers, automatic machine guns, sniper rifles and anti-tank mines were also seized, it said.