The Twitter account for U.S. Central Command was hacked on Monday, with pro-ISIS messages plastering the account's profile.
The first message was posted at 12:29 p.m. ET, with the words "AMERICAN SOLDIERS, WE ARE COMING, WATCH YOUR BACK. ISIS." and the hashtag "#CyberCaliphate."
The profile's image was replaced with a photo that includes the text "i love you isis." Just before 1 p.m. ET profile and banner images were reverted to their default.
The FBI said on Monday it was working with the Department of Defense to investigate the hacking of the Twitter and YouTube accounts of the U.S. military command that oversees operations in the Middle East.
Around 1:09 p.m. ET the Twitter account was suspended.
A YouTube page labeled as belonging to Centcom was also apparently hacked. By 1:30 p.m. ET, that page had been blanked.
"We can confirm that the U.S. Central Command's Twitter and YouTube accounts were compromised earlier today. We are taking appropriate measures to address the matter," a defense official told NBC News.
Later tweets included images of what were apparently spreadsheets labeled as containing the contact info and home addresses of retired U.S. army generals.
Other tweets claimed to include military plans from Pentagon networks. One such image showed a map of China with labels of different military assets. Another supposed Pentagon image featured a map of North Korea with labels for nuclear facilities.
Government officials told NBC News that the Twitter and YouTube accounts are not classified, and that none of the information posted by the hackers was actually classified—the names and contact information are "official use only," they said.
The slides containing information on China and North Korea were not military, the officials told NBC, with some of them coming from MIT.
A U.S. Department of Defense official told NBC News "this is clearly embarrassing, but not a security threat."
Press Secretary Josh Earnest said Monday afternoon the White House was monitoring the incident.
Another message read "ISIS is already here, we are in your PCs, in each military base."
The organization "CyberCaliphate" has previously hacked twitter accounts of U.S. media outlets, including The Albuquerque Journal and Maryland's WBOC 16, but Monday's was the highest-level attack as yet attributed to the group.
—NBC News and Reuters contributed to this report.