NATO says four of its service members were killed by enemy forces Sunday during a joint military operation in southern Afghanistan.
The international coalition did not reveal the nationalities of the service members. However, various reports say all four were from the United States and were killed by a roadside bomb.
Such bombs have become one of the top killers of Afghan and foreign soldiers, as well as civilians.
The U.S.-led NATO troops are winding down their operations as they prepare to withdraw by the end of next year.