The US Central Command Twitter account appears to have been hacked by supporters of ISIS.
The hackers claim to have leaked the names and addresses of US Army generals.
One message said: "American soldiers we are coming, watch your back."
"We won't stop! We know everything about you, your wives and children."
They also published apparent intelligence surveillance of Chinese and North Korean military plans and positions.
A US defence official has told NBC News that the account has "clearly been hacked."
The CENTCOM YouTube channel has also seemingly been compromised.
The apparent hacking came as President Obama prepared to announce new proposals to protect the country's cybersecurity.