WASHINGTON — An American military helicopter crashed Thursday near the city of Qaim in western Iraq, killing some of the seven service members aboard, United States officials said.

It was unclear why the aircraft, an HH-60 Pave Hawk, went down, the officials added. They did not rule out ground fire, and they could not confirm how many people had been killed.

One official said the helicopter was not on a combat operation but was ferrying troops.

Maj. Adrian J. Rankine-Galloway, a Pentagon spokesman, said Thursday night that rescue personnel had been deployed and that the crash, in Anbar Province, near Syria, was under investigation.

Ahmed al-Mahilawi, the mayor of Qaim, said that the helicopter crashed about 20 miles southeast of the town center, near a phosphate factory and railway station. The American military uses a base in the area.