The Pentagon on Friday announced a 15-6 investigation into the deaths of two Army Rangers killed in a firefight with ISIS forces in Afghanistan on April 27, citing a possible “friendly fire” incident.

The two Rangers were killed in eastern Nangarhar province, near the same area the U.S. Air Force dropped the 21,600-pound Massive Ordnance Air Blast (MOAB) bomb on April 13.

According to Army Times, the Rangers had partnered with local Afghan security forces for a crucial raid as part of a larger campaign to root out and neutralize pockets of ISIS fighters throughout the region.

“In the beginning of what was an intense three-hour firefight, it is possible these Rangers were struck by friendly fire,” Pentagon spokesman Capt. Jeff Davis said.

U.S. Forces Afghanistan also released a detailed statement describing the circumstances of the firefight and lauding both the Rangers and Afghan Special Security Forces for their “exemplary” performance:

Within a few minutes of landing, our combined force came under intense fire from multiple directions and well-prepared fighting positions. Nevertheless, our forces successfully closed on the enemy, killed several high-level ISIS-K leaders and upwards of 35 fighters. If confirmed, the death of the Emir and his associated will significantly degrade ISIS-K operations in Afghanistan and help reach our goal of destroying them in 2017.

Based on our reports from forces on the ground, the engagement was close-quarters from multiple compounds. Air strikes were used in self-defense to enable our operations and to medically evacuate the wounded Rangers. We do not have any indication there were civilian casualties as a result of this operation.

The Rangers killed were identified by the Pentagon as Sgt. Joshua P. Rodgers, 22, and Sgt. Cameron H. Thomas, 23. Both soldiers were assigned to the 3rd Battalion, 75th Ranger Regiment out of  Fort Benning, Georgia.