The Twitter account and YouTube account for US Central Command (CENTCOM) were suspended on Monday after they were hacked by ISIL sympathizers, defense officials said.
During a regular briefing, White House Press Secretary Josh Earnest said the administration was "obviously looking into" the incident but did not elaborate.
"We can confirm that the US Central Command Twitter account was compromised earlier today. CENTCOM is taking appropriate measure to address the matter," a defense official said.
Tweets were published with apparent warnings from ISIL along with links and Pentagon documents that reveal contact information for members of the US military.
The first tweet, published on Monday afternoon, read: "AMERICAN SOLDIERS, WE ARE COMING, WATCH YOUR BACK. ISIS." "CyberCaliphate" and "i love you isis" were displayed in white letters against a black screen atop the Pentagon Twitter page.
On the CENTCOM YouTube page, ISIL propaganda videos appeared depicting militant fighters.
The group also claimed to have obtained and released classified documents, but defense officials and Earnest said no classified information was compromised by the hacks.