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.

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.