Cameron said the British were not informed of the Algerian strike against the militants that began early Thursday, saying he only learned of it while on the phone with his Algerian counterpart. He said the Algerians insisted they had to act fast.
‘‘They judged there to be an immediate threat to the hostages,’’ he said.
A senior French official, who spoke on the condition of anonymity to address sensitive issues, said that Algerian authorities have not been forthcoming about tallies of the dead and rescued.
The Mauritanian news agency ANI, which has been in contact with the extremists who have asserted responsibility for the siege, said the group has offered to release its remaining American hostages in exchange for two high-profile prisoners being held in the United States.
ANI said the militants are seeking the release of the Pakistani scientist Aafia Siddiqui, convicted in a U.S. court in 2010 of the attempted murder of U.S. personnel in Afghanistan, and Egyptian Omar Abdel Rahman, the blind sheik convicted on terrorism charges.
The news agency also quoted a spokesman for the ‘‘Masked Brigade,’’ the Islamist group allegedly behind the attack on the gas complex. The group was affiliated with the umbrella organization known as al-Qaeda in the Islamic Maghreb (AQIM), but it reportedly broke with AQIM last month, according to terrorism experts in France.
Quoting unnamed sources, the Mauritanian news agency described the hostage takers as being from Algeria, Canada, Mali, Egypt, Niger and Mauritania.
The spokesman linked the attack to Western efforts to help the government of Mali fight Islamist insurgents and warned that the group would carry out ‘‘more operations.’’ He called on Algerians to stay away from the installations operated by foreign companies, because ‘‘we will spring up where nobody expects it,’’ the news agency said.
The U.S. military said Friday that one of its medical planes flew to Algeria to evacuate between 10 and 20 freed or rescued hostages. The former hostages will be transported to ‘‘a U.S. facility’’ in Europe, said Tom Saunders, a spokesman for the U.S. Africa Command, which is based in Stuttgart, Germany.
One Algerian engineer told the France Info radio station on Friday that the captors were interested only in the foreign employees. ‘‘They came into the bedrooms,’’ one said. ‘‘They broke down the doors. They were shouting: We’re only looking for the expatriates! The Algerians can leave! They rounded up the expats. . . . They tied them up.’’
Birnbaum reported from Berlin, and Faiola from London. Edward Cody in Paris, Sari Horwitz in Washington and Craig Whitlock and Eliza Mackintosh in London contributed to this report.