Six U.S. soldiers died in a helicopter crash in southern Afghanistan Tuesday.
NATO said it was the largest death toll in a single incident to hit the International Security Assistance Force in months. Officials say there were no reports of insurgent gunfire at the time of the crash, which happened in Zabul province.
"The cause of the crash is under investigation," a statement said. "However, initial reporting indicates there was no enemy activity in the area at the time."
A Pentagon official told VOA that one U.S. soldier survived and is injured. The cause of the crash appears to be engine failure, the official said.
The Pentagon is withholding the identity of the dead until 24 hours after next of kin are notified.
Some news reports said the helicopter was a Sikorsky UH-60 Black Hawk. But the Pentagon did not release the type of aircraft.
Crashes involving NATO aircraft are not unusual and the Taliban often claims responsibility.
In 2011, the Taliban claimed it downed a Chinook helicopter over Wardak province, killing 38 people, most of them Americans.