American troops were killed on Monday when a suicide bomber attacked a joint NATO-Afghan patrol near Bagram air base in Afghanistan, a U.S. official told Reuters, speaking on the condition of anonymity.

NATOs Resolute Support mission had said earlier that six of its service members were killed in the attack but did not name their nationalities.

The U.S. official declined to say how many Americans were killed, and it was unclear if anyone other than U.S. forces died in the attack.