KABUL, Afghanistan  — A helicopter crash killed two NATO service members in eastern Afghanistan on Monday, while a third died in an insurgent attack in the south, the U.S.-led coalition said.

Authorities are investigating the cause of the crash, but initial reports indicate there was no enemy activity in the area at the time the helicopter went down, the coalition said.

No further details about the crash in the east or the insurgent attack in the south were released.

The deaths raised the number of NATO troops who have been killed in Afghanistan this year to 172.

Also Monday, a second coalition aircraft crashed in eastern Afghanistan, but no fatalities were reported. The coalition said this incident was not related to the helicopter crash that also occurred in the east.

Officials are trying to determine why the aircraft went down, but initial reports indicate there was no enemy activity in the area. There were no reports of civilians being harmed or property damaged during the incident. The coalition transported the aircraft’s crew and passengers to a nearby base for evaluation.