The Twitter and YouTube accounts of the US military command have been hacked by a group claiming to back Islamic State.
One message said: "American soldiers, we are coming, watch your back."
It was signed by Isis, another name for the Islamic State.
Some internal military documents also appeared on the Centcom Twitter feed.
Centcom said it was taking "appropriate measures".
The Twitter account, which usually provide updates on strikes against IS, was later taken down.
