A current U.S. official and a former senior Obama administration official say that means the American training mission at the air field in Balad has been grounded indefinitely.
Twelve U.S. personnel who were stationed at Balad were the first to be evacuated. Several hundred American contractors are still waiting to leave.
They have been training Iraqi forces to use fighter jets and surveillance drones.
Other U.S. contractors at a tank training ground in the city of Taji (TAH'-jee) is still ongoing for now.
The officials spoke on condition of anonymity because they refused to be named in discussing the sensitive situation.