"Tragically we now know that three British nationals have been killed and a further three are believed to be dead and a further British resident is also believed to be dead," Cameron said in a televised statement.

"The priority now must be to get everybody home from Algeria ... and I have spoken this morning to our ambassador who is in Algiers and this morning will be going again to the south of the country to help coordinate that absolutely vital activity."

Foreign Secretary William Hague said shortly after Cameron spoke that 22 Britons who had been caught up in the hostage drama had flown home on charter flights organized by the government or by BP.

Cameron told Parliament on Friday he was "disappointed" Algeria had given him no advance warning of the operation to rescue hostages at the plant, but on Sunday he thanked Algeria for its actions.

"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 this vicious and cowardly attack," he said.

"We should recognize all that the Algerians have done to work with us and to help and coordinate with us. I'd like to thank them for that. We should also recognize that the Algerians too have seen lives lost among their soldiers."

Asked whether the threat from militant groups in North Africa was as serious as the one that had once existed in Afghanistan, Cameron said: "It is different in scale but there are similarities.

"What we face is an extremist Islamist violent al-Qaida-linked terrorist group, just as we had to deal with in Pakistan and Afghanistan, so the world needs to come together to deal with this threat in North Africa."

Seeking missing ones

Colombian President Juan Manuel Santos said on Saturday that a Colombian man who lived in London with his family had been killed. He was named as BP employee Carlos Estrada. Japanese engineering firm JGC Corp said 10 of its Japanese and seven of its foreign workers remained unaccounted for.

JGC confirmed the safety of 61 of its 78 workers at the In Amenas facility that was stormed at dawn on Wednesday by militants from "Signatories in Blood", a group demanding an end to French military intervention in Mali.

"But the safety of the remaining 10 Japanese and seven foreign workers is yet to be confirmed," a JGC spokesman said in Tokyo.

Authorities in Kuala Lumpur said JGC had confirmed one of two Malaysians still unaccounted for is dead. The fate of the other is unknown.

Reuters-AFP