KABUL/WASHINGTON (Reuters) — Two U.S. soldiers and an Afghan soldier were killed when an individual in an Afghan uniform opened fire on them with a machine gun in eastern Afghanistan, the U.S. military and two senior Afghan officials said on Sunday.

The shootout on Saturday wounded six U.S. service members and three Afghan soldiers.

The fire fight broke out after a combined U.S. and Afghan force completed a “key-leader engagement” at the administrative headquarters of Nangarhar province’s Shirzad district, a spokesman for U.S. forces in Afghanistan said.

The Taliban has not claimed responsibility for the attack and senior officials were investigating if it was an insider attack — often known as “green-on-blue” attacks that have been a regular feature of the conflict in Afghanistan.

Sohrab Qaderi, a provincial council member in Nangarhar, said the attacker was killed in the clash. He said the Islamist fighter had infiltrated the Afghan security forces involved in the joint operation, but did not say which group the militant belonged to.