A U.S. military general on Tuesday said "unintentional human errors" led to the deadly coalition bombing of Syrian-aligned forces near Deir Ezzor on Sept. 17.
U.S. Air Force Brig. Gen. Richard Coe, the investigating officer, called the bombing, which occurred during a U.S.-Russia brokered ceasefire, "regrettable."
Coe said the coalition forces who participated in the bombing — which included U.S., Australian and Danish forces — believed they were striking Islamic State in Iraq and Syria forces.
One factor in the error was that the forces on the ground behaved like ISIS fighters, and were not wearing uniforms, flags or insignias, Coe said. One intelligence analyst expressed skepticism that the forces on the ground were ISIS fighters, but it was not widely distributed.
Another factor was the U.S. military giving Russian forces erroneous information in advance of the bombing.
Over a hotline set up to avoid mid-air collisions, the U.S. notified the Russians that the coalition would be striking near Deir Ezzor, but gave a strike location that was nine kilometers off.
Coe said it was "possible" that had the U.S. passed the right location to the Russians, they would have said Syrian-aligned forces were in the area.
Another factor that contributed to the scale of the attack, which killed more than 15, was that the U.S. point of contact for the Russians could not be reached for 27 minutes.
After the bombing began, the Russians called the hotline but could not reach the designated point of contact, and said they would call back. After calling back, they waited on the line until they finally reached the person, 27 minutes after the bombing began.
Coe said it was the first time that the U.S. had given Russia advance notice of the bombing. The coalition employed F-16s, A-10s, F/A-18s and drones in the strike.