A US security company helicopter crashed as it flew over a dangerous Sunni neighborhood in the central Baghdad where insurgents and Iraqi security troops fought a prolonged gunbattle, and a US official said five American civilians on board were killed. A senior Iraqi military official said Tuesday the aircraft was shot down, but this was disputed by a US military official in Washington. The Iraqi said the helicopter was hit by a machine gunner over the Fadhil neighborhood on the east side of the Tigris River, while the American official said there was no indication in initial reports that the aircraft, owned by Blackwater USA, had been shot down. A US official in Baghdad had said there was no information to substantiate reports that the bodies had been shot. All the officials demanded anonymity because the details had not been made public. The Americans said they did not know what caused the aircraft to crash.