A Marine who was killed in Iraq over the summer died during a combat operation from enemy actions, not friendly fire, according to military officials.

The Pentagon initially concluded the Aug. 10 death of Marine Gunnery Sgt. Scott A. Koppenhafer was by enemy small arms fire near Qanus Island in Iraq, the Marine Corps Times reported. His death was the first American combat casualty since U.S. forces returned to the country in 2014 to battle the Islamic State.

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Soon after announcing the cause of death, the Pentagon began looking into whether Koppenhafer, 35, was accidentally shot by U.S. or Iraq forces instead.

“There is no evidence that suggests Iraqi Partner Forces engaged U.S. or Coalition forces on this operation," officials with Operation Inherent Resolve told the Times in an emailed statement Tuesday. "The deaths and injuries were incurred in the line of duty.”

Koppenhafer, of Mancos, Colo., was assigned to the 2nd Marine Raider Battalion based at Camp Lejeune, N.C., at the time of his death.

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He was part of a joint U.S.-Iraqi task force established to take back terrority taken by ISIS after the group took control of the city of Mosul in northern Iraq.