The group claiming to have masterminded the storming of the Algerian gas plant warned of more attacks against any country backing France's military intervention in neighbouring Mali.

In a statement, the Masked Brigade said: "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,"

It came as the death toll from the terrorist siege at the In Amenas natural gas plant in the Sahara climbed to more than 80.

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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.

Special forces stormed the plant on Saturday to end the four-day siege, moving in to thwart what the government said was a plot by the Islamist militants to blow up the complex and kill all their hostages with mines laid throughout the site.

Algeria said after the assault by government forces at least 32 extremists and 23 hostages were killed.

Yesterday Algerian bomb squads sent in to blow up or defuse the explosives found 25 more bodies, said a security official.

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

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," Prime Minister David Cameron said. Three Britons were killed and another three were feared dead.

Two Scottish families have been told relatives were among the victims, but names have not been made public yet.

The dead hostages were also known to include at least one American as well as Filipino 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 on 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 yesterday the attack was payback against Algeria for allowing overflights of French aircraft headed to Mali and for closing its long border with the country. In an earlier communication, the group 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, favouring 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 Mohammed Said said.

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," he said. 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 organise a prisoner swap.

"You see our demands are so easy, so easy if you want to negotiate with us," al-Nigiri said in the recording broadcast by Algerian television. "We want the prisoners you have, the comrades who were arrested and imprisoned 15 years ago. We want 100 of them."

In another phone call, al-Nigiri said that half the militants had been killed by the Algerian army on Thursday and that he was ready to blow up the remaining hostages if security forces attacked again.

An organisation that monitors videos from radicals posted one showing al-Nigiri with what appeared to be an explosive belt around his waist.

The Algerians' use of forced raised an international outcry from some countries worried about their citizens.

But French foreign minister Laurent Fabius said today on French television: "The terrorists ... they're the ones to blame."

David Plouffe, a senior adviser to President Barack Obama, said al Qaida and al Qaida-affiliated groups remained a threat in North Africa and other parts of the world and the US was determined to help other countries destroy those networks.

Speaking on Fox News Sunday, Mr Plouffe said the tragedy in Algeria showed once again "that all across the globe countries are threatened by terrorists who will use civilians to try and advance their twisted and sick agenda".

The Philippines' Foreign Affairs Office said today six Filipino workers were among hostages killed by the militants.

Foreign affairs spokesman Raul Hernandez said 16 Filipinos had been accounted for and four others were still missing.

He said the information came from Algerian authorities.