"We mourn the loss. These are three great people and just a terrible thing. We will retaliate," Trump told reporters as he left the White House to attend the Army-Navy football game.

The Pentagon said the two soldiers and the interpreter were ambushed by a lone gunman in the city of Palmyra while taking part in ongoing counterterrorism missions. The gunman, who was already under investigation for his ties to ISIS, was killed, according to a U.S. official.