Hackers claiming allegiance to the Islamic State took control of the social media accounts of the U.S. military's Central Command on Monday, posting threatening messages and propaganda videos, along with some military documents.

The command's Twitter and YouTube accounts were eventually taken offline, but not before a string of tweets and the release of military documents, some of which listed contact information for senior military personnel. Centcom said in a statement that the accounts were "compromised" and the FBI said it is investigating the incident along with the military. It appears that no classified information was taken or released.

"CENTCOM's operation military networks were not compromised and there was no operational impact to U.S. Central Command," the statement said. "CENTCOM will restore service to its Twitter and YouTube accounts as quickly as possible. We are viewing this purely as a case of cyber vandalism."

The U.S. and the Islamic State have waged a propaganda battle online for the better part of a year, after the militants rose to prominence and seized broad swaths of territory in Iraq and Syria. Centcom oversees the U.S. military campaign against the group, and frequently posts videos of airstrikes on the same accounts hacked Monday.

Twitter accounts sympathetic to the militants have distributed graphic image of beheadings and other violence along with threats, while the U.S. has tried to use social media to expose the Islamic State as a group of fanatics and oppressors.

The hack of Centcom appeared designed to embarrass the U.S. military. Virtually all of the documents posted seem to already have been publicly available online. They included what appeared to be U.S. Army rosters with names and contact information for a variety of soldiers, including Gen. Martin E. Dempsey, chairman of the Joint Chiefs of Staff.

The hacking Monday came the same day that President Obama called for new cybersecurity measures designed to protect the online privacy of consumers and students. The individuals who took over the Centcom accounts did not reference that, but the timing was noted repeatedly on social media.

The first rogue tweet was posted about 12:30 p.m. on the Centcom account, which was not suspended for about another 40 minutes. The background and profile photo of the Twitter account were both changed to show a militant and the phrases "CyberCaliphate" and "i love you isis," using one of the acronyms for the militant group.

One tweet said the militants were already in American computers, showing the odd image of an American soldier tending to what appeared to be a goat in a military office.

"AMERICAN SOLDIERS, WE ARE COMING, WATCH YOUR BACK," another tweet said.

Analysts said the hack should not be over-dramatized.

"Let's remember this is a social media account," said Peter Singer, a strategist and analyst with the New American Foundation in Washington. "This is not a military command and control network. This is not a network that moves classified or even non-classified internal information back and forth. Essentially what they did is for several minutes take control of the megaphone."

White House Press Secretary Josh Earnest said the Obama administration is "examining and investigating the extent of the incident."

"This is something we are obviously looking into and something we take seriously," he told reporters Monday. He said that there is a "pretty significant difference" between "a large data breach and the hacking of a Twitter account."

The Centcom YouTube page was also hacked, with two Islamic State propaganda videos added to the page and the same "CyberCaliphate" banner posted. The YouTube account was eventually "terminated due to repeated or severe violations" of YouTube's guidelines, the Website said.

Central Command also maintains Facebook accounts, but it appears they were not affected.

It is not clear whether the hackers are actually with the Islamic State, sympathizers, or simply pulling a prank on the Pentagon. A group using the same "CyberCaliphate" name and photo seen in the hack against Centcom recently hacked the Twitter accounts of the Albuquerque Journal in New Mexico and the WBOC-TV station in Salisbury, Md.

Twitter offers a two-step verification process to sign into an account that makes it secure, but it is not required. Without it, a Twitter account typically requires only an email address and a password.

J.M. Berger, an analyst and non-resident fellow with the Brookings Institution, said there is reason to believe it could be someone affiliated directly with the Islamic State.

"ISIS has a team of hackers who are very deeply involved in ISIS the organization," said Berger, author of the forthcoming book "ISIS: The State of Terror."

"They have been practicing and recruiting for a while, and this has been going on for months and months," Berger said.

Singer said the incident amounts to a public relations victory for the Islamic State, even if they were not directly involved. Embarrassing the U.S. government "is a feather in their cap in terms of pulling off something that other groups have not been able to do, no matter how silly it is at the end of the day."