The Twitter and YouTube accounts of the US military command have been hacked by a group claiming to back the Islamic State.
Some internal military documents appeared on the Centcom Twitter feed.
The Twitter account, which usually provides updates on strikes against IS, was later taken down.
White House press secretary Josh Earnest says they are investigating the extent of the incident.
"I can tell you that this is something that we're obviously looking into and something that we take seriously. However a note of caution to folks who are covering this story, there's a pretty significant difference between what is a large date breach and the hacking of a twitter account."
The hack happened as President Barack Obama was giving a speech on cyber security in which he said the internet creates "enormous vulnerabilities".
