Six Americans have been killed in a helicopter crash in southern Afghanistan, Fox News confirms.

One person on board the aircraft was injured and survived, two U.S. defense officials told The Associated Press on condition of anonymity because they were not authorized to speak on the record.

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.

The service members were part of the International Security Assistance Force.

NATO says there is currently no fighting in the area.

"The cause of the crash is under investigation, however initial reporting indicates there was no enemy activity in the area at the time," a NATO statement said.

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.

According to Reuters, the incident is the largest death toll to hit the international force in months.

Aircraft crashes are not uncommon in Afghanistan.

The worst such incident was in August 2011, when the Taliban shot down a transport helicopter, killing all 38 people on board including 25 U.S. special operations forces, Reuters reported.

About 84,000 NATO-led troops are serving in Afghanistan, including about 60,000 from the U.S. That number is expected to be reduced to about 10,000 by 2015, the report said.

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.

Fox News' Conor Powell and The Associated Press contributed to this report.

Click for more from Reuters.