An extremist group claimed responsibility for the rare attack on one of oil-rich Algeria's energy facilities, saying it came in revenge for Algeria's support for France's military operation against al-Qaeda-linked rebels in neighboring Mali. The extremists said they were holding 41 foreigners from the energy complex, including seven Americans.
The group - Katibat Moulathamine, or the Masked Brigade - phoned a Mauritanian news outlet to say that one of its affiliates had carried out the operation at the Ain Amenas gas field, 800 miles south of Algiers, and that France must cease its intervention to ensure the hostages' safety.
BP, together with the Norwegian company Statoil and the Algerian state oil company Sonatrach, operates the gas field. A Japanese company, JGC Corp, provides services as well.
In Rome, Defense Secretary Leon E. Panetta declared that the United States "will take all necessary and proper steps" to deal with the attack.
"We reject all negotiations with the group," Algeria's top security official, Interior Minister Daho Ould Kabila said on national television.
Hundreds of Algerian workers at the plant were taken hostage but were gradually released unharmed in small groups.
Kabila said the roughly 20 well-armed gunmen were from Algeria, operating under orders from Moktar Belmoktar, al-Qaeda's strongman in the Sahara.
A close associate of Belmoktar blamed the West for France's recent air and ground intervention against Islamist fighters in Mali.
"It's the United Nations that gave the green light to this intervention, and all Western countries are now going to pay a price," Oumar Ould Hamaha told the Associated Press by phone.