The Twitter account of the military's U.S. Central Command was taken over Monday by hackers claiming to be working on behalf of the Islamic State militants.
American and coalition fighters are launching airstrikes against the group known as ISIS (Islamic State in Iraq and Syria), or ISIL.
Canada is participating in the mission in Iraq by conducting airstrikes and helping to train Iraqi soldiers.
The first message on the hacked account appeared around 12:30 p.m. ET. "American soldiers, we are coming, watch your back," read one message. Other postings appeared to list names and phone numbers of military personnel as well as PowerPoint slides and maps.
The images did not appear to come from classified information.
Shortly after the messages appeared, the @CENTCOM Twitter account was suspended along with the YouTube channel. The military unit's YouTube account was also apparently hacked and propaganda videos were added.
White House spokesman Josh Earnest told reporters that officials are looking into what happened and it is being taken seriously. He noted that Centcom's databases and website were not hacked, only social media website accounts.
"There is a pretty significant difference between what is a large data breach and the hacking of a Twitter account," he said. "We're still examining and investigating the extent of this incident."
The U.S. Central Command's area of responsibility includes Syria, Iraq, Afghanistan, and other countries in that region.