The military says the attack took place on Saturday but provided no other information about the incident.

Earlier this month, a suicide bomber attacked a joint Afghan-NATO patrol in the region, killing at least 14 people. The Taliban claimed responsibility.

On Friday, U.S. Defense Secretary Leon Panetta said Afghanistan's president needed to show the international coalition troops who are fighting and dying in his country some gratitude instead of criticizing them. 

Panetta was responding to Afghan President Hamid Karzai's remarks a day earlier, in which he said the U.S. was failing to go after Pakistan-based militants and was instead concentrating on the insurgents in Afghanistan.

Panetta said, "I think it would be helpful if the president every once and awhile expressed his thanks for the sacrifices that have been made by those who have fought and died for Afghanistan, rather than criticizing them."

Tensions between Washington and Kabul have escalated over an increase in insider attacks, in which Afghan security force members, or militants posing as security force members, turn their guns on coalition troops.