The eight troops and contractor killed by a man wearing an Afghan Air Force uniform were confirmed to be American, a well-placed military source said on Wednesday, the worst single-day U.S. death toll in nearly three years.

While it would not officially release the nationalities of the troops, the U.S.-led coalition issued a statement condemning the attacks. “Today, NATO Training Mission Afghanistan suffered a tragic loss from an attack, which occurred this morning, resulting in the deaths of nine coalition trainers,” said Lt. Gen. William Caldwell, commander of NATO’s training mission in Afghanistan, in a statement. “I wish to convey our heartfelt condolences to the families of the trainers killed today.”…

It’s the highest death toll in one day since the battle of Wanat in eastern Afghanistan in July 2008, an attack that killed nine Americans and wounded 27.