Baghdad, Iraq ? A U.S. security company helicopter crashed Tuesday as it flew over a dangerous Sunni neighborhood in the central Baghdad where insurgents and Iraqi security troops fought a prolonged gunbattle, and a U.S. official said five American civilians on board were killed.

A senior Iraqi military official said the aircraft was shot down, but this was disputed by a U.S. 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 U.S. 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.

Crash details

Blackwater USA confirmed that five Americans employed by the North Carolina-based company as security professionals were killed. The statement from spokeswoman Anne Tyrrell did not provide identities or any details of the fighting.

The New York Times reported the helicopter went down as it came under attack and plummeted to the pavement through a tangle of electrical wires, but it was unclear if the crash resulted from gunfire, the wires or an effort to land.

Quoting unnamed American officials, the newspaper said the helicopter’s four-man crew was killed along with a gunner on a second Blackwater helicopter. It said one military official said that at least four of the victims had suffered gunshot wounds to the head, raising the prospect that some of them had been shot on the ground.

Witnesses in the Fadhil neighborhood told The Associated Press that they saw the helicopter go down after gunmen on the ground opened fire, possibly striking pilot or co-pilot or both. Accounts varied, but all were consistent that at least one person operating the aircraft had been shot and badly hurt before the crash.

The helicopter was believed to have been flying escort above a VIP convoy on the ground as it headed away from the heavily fortified Green Zone to an undisclosed destination.

A report in the Washington Post, quoting unnamed U.S. officials, said one of the Blackwater victims was killed as he traveled with the convoy on the ground.

Blackwater USA provides security for State Department officials in Iraq, trains military units from around the world, and works for corporate clients.

Before Tuesday’s crash, at least 22 employees of Blackwater Security Consulting or Blackwater USA had died in Iraq as a result of war-related violence, according to the Web site iCasualties.org, which tracks foreign troop fatalities in Iraq. Of those, 20 were Americans, and two were Polish.

Second crash in four days

The crash of the small surveillance helicopter, believed to be a version of the Hughes Defender that was developed during the Vietnam War, was the second associated with the U.S. war effort in Iraq in four days.

A U.S. Army Blackhawk helicopter went down Saturday northeast of Baghdad, killing all 12 service members on board. The American military in Baghdad has refused to confirm a report by a Pentagon official that debris at the crash site indicated the helicopter was shot out of the air by a surface-to-air missile.

Relatively few U.S. aircraft have been shot down during the war despite hundreds, perhaps thousands of flights above Iraq. Helicopters typically flow fast and low over populated areas, making it extremely difficult for militant fighters to draw a bead with shoulder-fired missiles. U.S. fighter jets normally fly at very high altitudes and usually can be heard screaming through the skies but remain invisible to the naked eye.

Civilian aircraft that serve Baghdad International Airport use avoidance techniques that included landing in a steep, circular descent from nearly straight overhead the runways. Takeoffs are achieved with the same technique until passenger jets are out of missile range.

The Blackwater aircraft was at least the 14th helicopter to go down since the war began in March 2003.