A big battled raged Monday in central Baghdad after insurgents hijacked two buses and kidnapped at least 15 passengers, police said. At least three policemen had been killed and four wounded, authorities said. The small buses where traveling through the Fadhil neighborhood, a Sunni enclave in central Baghdad, when they were waylaid by unidentified gunmen in three cars at 10:15 a.m. The insurgents then abducted at least 15 passengers and took them to a nearby abandoned government building, a police officer said on condition of anonymity because he was not authorized to talk to reporters. The buses were heading from Baghdad's central Bab al-Mudham bus station to the city's eastern Shiite neighborhoods. The fighting began when Iraqi security forces reached the scene about 30 minutes later, police said. According to Iraqi police, at least two US helicopters were hovering overhead and US forces had taken up positions near the fighting, but were not directly involved. Sunni insurgents have repeatedly clashed with US and Iraqi forces in the Fadhil area, which is also known for its high crime rate.