A helicopter crash in Helmand province in southern Afghanistan killed six U.S. Marines, the NATO military command in Kabul told NBC News early Friday.
Officials said there were no signs of enemy activity at time of crash, which is still under investigation.
The Marines have a substantial presence in Helmand province.
"We are still in the process of gathering more information on the incident," an official told Reuters news agency. He declined to give any details of the crash until the families of those on board had been informed.
It is the worst crash since last August when 30 soldiers, including 22 elite Navy SEAL commandos, died when their helicopter came down in eastern Afghanistan.
The Helmand helicopter crash occurred on the same day seven civilians were killed outside a crowded gate at Kandahar Air Field, a sprawling base for U.S. and NATO operations, after a suicide attacker set off a vehicle laden with explosives. The Taliban claimed responsibility, saying they were targeting a NATO convoy.