Officials said al-Qaida in the Islamic Maghreb was behind the attack, and may have done so with the help of fighters loyal to Moktar Belmoktar, a terrorist leader who has claimed responsibility for the Algerian attack.
CNN said if the two factions reunited for the attack, it would indicate cooperation and communications among al-Qaida affiliates in North Africa.
Officials said they believe some of the attackers came into Algeria training camps from Libya and the attack was relatively sophisticated.
"It took planning to select and case the facility, and coordinate to attack it. They had to penetrate the perimeter security and take hostages. That doesn't just happen," one official told CNN.
Defense Secretary Leon Panetta vowed to go after the perpetrators if the officials find out who they are, CNN reported.
Exploding whale video goes viral on Internet
Trader Joe's: Car crashes into Long Island store, injuring 11