A U.S. military investigation has concluded that U.S. airstrikes in Afghan in November killed 33 civilians and 27 wounded others, but that strikes were in self-defense, and that the deaths of innocents were regrettable but unavoidable.

“Regardless of the circumstances, I deeply regret the loss of innocent lives,” said Gen. John Nicholson, U.S. Afghanistan commander, in a Thursday morning statement. “On this occasion the Taliban chose to hide amongst civilians and then attacked Afghan and U.S. forces.”