WASHINGTON (Reuters) – A U.S. Army artillery “mishap” was responsible for the deaths of two U.S. service members in northern Iraq over the weekend, a Pentagon official said on Monday.

Two U.S. service members were killed and five injured in northern Iraq on Sunday.

In a statement later on Monday the Pentagon identified those killed as Sergeant Allen Stigler Jr., 22, of Arlington, Texas, and Sergeant Roshain E. Brooks, 30, of Brooklyn, New York, both members of the 82nd Airborne Division Paratroopers.

The U.S. Army is investigating the incident, it said.

“An Army artillery section was conducting a counterfire mission against an ISIS mortar site when a mishap occurred, injuring seven soldiers,” Pentagon spokesman Colonel Robert Manning said, using an acronym for the Islamic State.

The Pentagon declined to provide further details and it was not immediately clear exactly what type of “mishap” took place.

The service members were part of a U.S.-led coalition fighting the Islamic State in Iraq.

Manning said there was no indication that Islamic State had anything to do with the deaths and the five injured troops did not suffer life-threatening injuries.