In this image made from video, a group of people believed to be hostages kneel in the sand with their hands in the air at an unknown location in Algeria. Algerian de-mining teams were scouring a gas refinery on Sunday, Jan. 20, 2013 that was the scene of a bloody four-day standoff, searching for explosive traps left by the Islamist militants who took dozens of foreigners hostage. The siege left at least 23 captives dead, and the American government warned that there were credible threats of more kidnapping attempts on Westerners. (AP Photo/Ennahar TV) ALGERIA OUT, TV OUT

ALGIERS, Algeria (AP) -- The death toll from the terrorist siege at a natural gas plant in the Sahara climbed past 80 on Sunday as Algerian forces searching the refinery for explosives found dozens more bodies, many so badly disfigured it was unclear whether they were hostages or militants, a security official said.

Algerian special forces stormed the plant on Saturday to end the four-day siege, moving in to thwart what government officials said was a plot by the Islamic extremists to blow up the complex and kill all their captives with mines sown throughout the site.

In a statement, the Masked Brigade, the group that claimed to have masterminded the takeover, warned of more such attacks against any country backing France's military intervention in neighboring Mali, where the French are trying to stop an advance by Islamic extremists.

"We stress to our Muslim brothers the necessity to stay away from all the Western companies and complexes for their own safety, and especially the French ones," the statement said.

Algeria said after Saturday's assault by government forces that at least 32 extremists and 23 hostages were killed. On Sunday, Algerian bomb squads sent in to blow up or defuse the explosives found 25 more bodies, said the security official, who spoke on condition of anonymity because of the sensitivity of the situation.

"These bodies are difficult to identify. They could be the bodies of foreign hostages or Algerians or terrorists," the official said.

In addition, a wounded Romanian who had been evacuated died, raising the overall death toll to at least 81.

"Now, of course, people will ask questions about the Algerian response to these events, but I would just say that the responsibility for these deaths lies squarely with the terrorists who launched a vicious and cowardly attack," British Prime Minister David Cameron said. Three Britons were killed and another three were feared dead.

On Monday, Philippine Foreign Affairs officials said six Filipinos were among the hostages killed. Spokesman Raul Hernandez told reporters that 16 Filipinos have been accounted for and four others are still missing.

The dead hostages were also known to include at least one American and French workers. Nearly two dozen foreigners by some estimates were unaccounted for.

It was unclear whether anyone was rescued in the final assault on the complex, which is run by the Algerian state oil company along with BP and Norway's Statoil.

Two private Algerian TV stations and an online news site said security forces scouring the plant found five militants hiding out and learned that three others had fled. That information could not be immediately confirmed by security officials.

Authorities said the bloody takeover was carried out Wednesday by 32 men from six countries, under the command from afar of the one-eyed Algerian bandit Moktar Belmoktar, founder of the Masked Brigade, based in Mali. The attacking force called itself "Those Who Sign in Blood."

The Masked Brigade said Sunday the attack was payback against Algeria for allowing over-flights of French aircraft headed to Mali and for closing its long border with Mali. In an earlier communication, the Brigade claimed to have carried out the attack in the name of al-Qaida.

Armed with heavy machine guns, rocket launchers, missiles and grenades, the militants singled out foreign workers at the plant, killing some of them on the spot and attaching explosive belts to others.

Algeria's tough and uncompromising response to the crisis was typical of its take-no-prisoners approach in confronting terrorists, favoring military action over negotiation. Algerian military forces, backed by attack helicopters, launched two assaults on the plant, the first one on Thursday.

The militants had "decided to succeed in the operation as planned, to blow up the gas complex and kill all the hostages," Algerian Communications Minister Mohamed Said told state radio.

Norwegian Foreign Minister Espen Barth Eide said the terrorists had tried to blow up the plant on Saturday but managed only to start a small fire. "That's when they started to execute hostages, and the special forces intervened," Eide said. Norway's Statoil said five Norwegians were still missing.

An audio recording of Algerian security forces speaking with the head of the kidnappers, Abdel Rahman al-Nigiri, on the second day of the drama indicated the hostage-takers were trying to organize a prisoner swap.

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