(NECN/NBC News: Anabelle Roberts, London) - Algerian special forces launched a final assault. Local media report the remaining seven hostages being held at the plant were executed, and their captors killed.
Defense Secretary Leon Panetta said the perpetrators will be hunted down.
"Just as we cannot accept terrorism attacks against our cities, we cannot accept attacks against our citizens and our interests abroad."
Video broadcast on Algerian television is said to have been shot on a cell phone by a hostage freed by the Algerian army walking to safety - past the bodies of those he once worked beside. NBC News has not been able to verify its authenticity.
Some hostages have talked of extreme brutality.
Abdul Rahman al Nigeri was the leader, according to some reports. It's thought there were forty militants linked to Al Qaeda in the Maghreb.
The plant was a joint venture between Norway's Statoil, Algeria's state owned oil company and BP.
Statoil has confirmed five of its workers are missing. BP says four staff members are unaccounted for.
BP has confirmed that one American survived, the plant manager Mark Cobb from Texas, but it's thought 23 hostages lost their lives in the desert.