Five British nationals and a UK resident were tonight believed dead or missing as the Algeria hostage crisis ended in a bloody and violent climax.
Foreign Secretary William Hague announced the latest causalities after Algerian special forces mounted a “final assault” on the remaining Islamist militants still holding out at the remote BP gas plant at In Amenas.
“On the basis of the information that we have this evening, we believe that there are five British nationals or one British resident who are either deceased or unaccounted for, in addition to the one fatality that we had already confirmed,” he said.
“We are working hard to get definitive information about each individual. We are in touch with all of the families concerned.”
David Cameron said that he had spoken to Algerian prime minister Abdelmalek Sellal, who confirmed that the four-day hostage crisis was “effectively ended”.
“I know that the whole country shares my sympathy and concern for everyone who has been caught up in this incident, and for their friends and families,” the Prime Minister said in a statement.
“It is our priority now to get people home as quickly as possible and to look after the survivors. Many are already home or on their way back.
“Let me be clear. There is no justification for taking innocent life in this way.
“Our determination is stronger than ever to work with allies right around the world to root out and defeat this terrorist scourge and those who encourage it.”
Seven hostages and 11 of the Islamist militants holding them were reported to have died in the final shoot-out in the vast desert complex close to the Libyan border.
The Algerian state news agency, APS, quoted an Algerian security source as saying that the hostages who died were killed by their captor.
The Algerian authorities were tonight removing explosives left by the militants who booby-trapped the plant before the final battle.
Mr Hague, speaking after chairing the second meeting of the day of the Government's Cobra emergencies committee, refused to be drawn into criticising the Algerian rescue operation, despite the death toll.
“I don't want to at this stage enter into criticism or judgment because there will be a lot to be learned yet about this operation,” he said.
“Our focus is very much on getting British nationals who have survived this ordeal and away from that area.”
Defence Secretary Philip Hammond said: “The loss of life as a result of these attacks is appalling and unacceptable. We must be clear that it is the terrorists who bear sole responsibility for it.”
Meanwhile, BP chief executive Bob Dudley said the company was “unable to confirm the location or situation” of four employees at In Amenas and had “grave fears” that they are likely to have suffered fatalities.
The British ambassador to Algiers, Martyn Roper, was tonight in In Amenas, alongside a UK consular team, after finally being granted permission to fly to the region.
The situation at the plant remains unclear and Mr Dudley said that it could be some time before they establish exactly what happened. Two BP employees suffered injuries although they are not life-threatening.
“Our focus remains on our colleagues, who we have not yet been able to locate, and on supporting their families through a time of agonising uncertainty. BP is a company that cares about its people. This is a difficult and sad time for us all,” he said.
He said 25 of the 56 BP workers in Algeria at the time of the attack have now left in a “staged process” of withdrawing all non-essential staff from the country.
Scotland's First Minister Alex Salmond said eight Scottish residents are confirmed safe and secure but said some of the workers still unaccounted for have family in Scotland or other connections to the country.
Earlier, the kidnappers, who call themselves “Those Who Sign in Blood”, told a Mauritanian news agency they were in contact with that they were holding seven foreigners: one British, three Belgians, two Americans and one Japanese.
The drama began on Wednesday when a group of about 30 heavily-armed militants mounted a dawn raid at the plant close to the Libyan border, seizing hostages from among the 700 Algerian and foreign workers at the site. Two workers, including one Briton, died in the initial assault.
The following day, Algerian special forces mounted an operation to take back the plant, to the initial dismay of the British and other governments who were not notified in advance despite offering assistance to the Algerian authorities.
The Algerians, however, insisted that they had to act immediately amid fears that the militants were about to flee into the desert, taking hostages with them.
By Friday APS reported that about 100 foreigners, from a total of 132, and 573 Algerians were freed, with a “provisional” figure of 12 hostages and 18 militants killed in the fighting, although the kidnappers claimed 35 foreigners died.
But it was also clear that a group of militants, still holding hostages, was continuing to hold out.
The kidnappers, part of the Masked Brigade - a terrorist splinter group led by the veteran jihadist, Mokhtar Belmokhtar, which broke away from al Qaida in the Islamic Maghreb - initially claimed the attack was in retaliation for the French military intervention in neighbouring Mali.
It was subsequently reported that they were demanding the release of two terrorists held in the US, including 1993 World Trade Centre bombing mastermind Omar Abdel Rahman, in return for the release of two US captives.
The plant at In Amenas is jointly operated by BP, Norwegian company Statoil and Algerian state oil company Sonatrach.
Despite the casualties among the hostages, an Algerian government source quoted by APS strongly defended the military operation, saying it prevented a “true disaster” which would have caused “immeasurable” human and material damage.
The rescue mission was carried out in “extremely complex circumstances” against terrorists armed with a huge arsenal of missiles, rocket launchers, grenades and assault rifles, the source said.
Swift action was the “only way to minimise or neutralise the deadly intent of the multinational terrorists - but not without the inevitable risks in all such situations”.
As freed hostages began to leave the plant, accounts emerged of their horrific treatment at the hands of the kidnappers.
One Algerian worker, who gave his name only as Chabane, described how from his hiding place he heard the militants speaking among themselves with Libyan, Egyptian and Tunisian accents. At one point, he said, they caught a Briton.
“They threatened him until he called out in English to his friends, telling them 'Come out, come out. They're not going to kill you. They're looking for the Americans',” he said.
“A few minutes later they blew him away.”
The family of British survivor Darren Matthews, from Saltburn-by-the-Sea in Cleveland, expressed their relief that he had escaped unhurt.
“We have been extremely worried about Darren and we are pleased and relieved to learn that he is safe and well,” they said in a statement released through the Foreign Office.
“We look forward to having him home soon. We ask that the media respect our privacy at this difficult time.”
In a statement tonight, the Algerian Interior Ministry said that a total of 23 hostages and 32 terrorists had been killed, and that 107 foreign workers and 685 local employees had been released.
It said that troops had recovered six machine guns, 21 rifles, two shotguns, two 60mm mortars with shells, six 60mm missiles with launchers, two rocket-propelled grenades with eight rockets and 10 grenades in explosive belts.
Labour leader Ed Miliband said his thoughts were with those who had lost loved ones in this “appalling act of terror”.
“The victims were people simply trying to make a living far from home and their families. People across Britain will be thinking of them and their families tonight,” he said.
“We support all efforts by the Government to identify those who planned this attack and bring them to justice.