Two U.S. Army Rangers killed during a raid on an Islamic State compound in Afghanistan earlier this week may have been killed by friendly fire, the Pentagon said Friday. An investigation has been opened into their deaths to determine whether they were killed by Afghan forces helping U.S. troops or other U.S. forces, Navy Capt. Jeff Davis said Friday. According to Davis, about 35 IS militants were killed during the hours-long firefight late Wednesday, and a top leader of the terrorist group’s affiliate in Afghanistan was suspected among the dead. “This was a dangerous mission and we knew this going in,” Davis told reporters. “Within minutes of the insertion the combined force came under intense fire from multiple directions. It was during these initial moments of the raid that the two Rangers were mortally wounded,” he said. The raid was conducted in Mohmand Valley in Nagarhar Province, the same area where the U.S. military dropped a massive bomb earlier this month. The two servicemen killed were identified as Sgt. Joshua Rodgers, 22, of Illinois, and Sgt. Cameron Thomas, 23, of Ohio.