WASHINGTON — Six U.S. service members were killed Tuesday when a helicopter crashed in southern Afghanistan, U.S. and NATO officials said.

One person on board the Black Hawk UH-60 was injured and survived, two U.S. defense officials said on condition of anonymity because they were not authorized to speak on the record. The aircraft was an Army helicopter from an Army unit, but officials have not yet confirmed the identities nor the service branches of the individuals, a third official said.

A statement issued by the NATO international military coalition said the crash was under investigation and that there was no insurgent activity in the area at the time of the crash.

In Washington, an official originally said the helicopter had experienced engine failure before the crash, but later said that it was unclear whether that was the case. According to initial reports, the troops had mechanical problems, came under fire after the crash and it was unclear whether any of the casualties were the result of enemy fire.

The deputy governor of southern Zabul province, Mohammad Jan Rasoolyar, said a NATO helicopter crashed in the remote district of Shajau and U.S. officials later confirmed that Zabul was the location of the U.S. crash.

This year, 109 members of the U.S. military have died in Afghanistan, out of a total of 139 members of the coalition.

The death toll has dropped significantly since the coalition handed over responsibility for security to Afghan forces last summer and coalition troops are now training and assisting.

By comparison, 394 foreign troops died last year, including 297 Americans.