A series of airstrikes begun Thursday have targeted ISIS strongholds as Yazidi minorities flee the Sunni Islamic militants on Mount Sinjar.
"Wherever and whenever (U.S.) personnel are facilities are threatened, it is my obligation ... to make sure they're protected," Obama said, not giving a timetable for future attacks.
"I don't think we're going to solve this problem in weeks. I think this is going to take some time," he added.
Obama said ISIS was able to advance as quickly as it has because of a weakly functioning Iraqi government.