30 hostages, including two Britons, died after Algerian forces defied international pleas for caution and stormed the In Amenas gas compound, which is deep in the Sahara desert, close to the Algerian border with Libya.
Following his chairing of an emergency Cabinet Office Briefing Room (COBR) meeting, the Prime Minister told the Commons that the initial attack on buses travelling from the BP gas plant, in which one Briton died, was “large, well co-ordinated and heavily armed” and appeared to be pre-planned.
Mr Cameron said he asked his Algerian counterpart, Abdelmalek Sellal to warn him if any action was planned, but he was not informed of yesterday's assault by Algerian military until it was under way. Offers of British help had reportedly been declined.
Mr Cameron told the Commons: “[Sellal] said that the terrorists had tried to flee, that they judged there to be an immediate threat to the lives of the hostages and had felt obliged to respond.”
He added: “This is a large and complex site and they are still pursuing terrorists and possibly some of the hostages in other areas of the site.
”The Algerian prime minister has just told me this morning that they are now looking at all possible routes to resolving this crisis.
Mr Cameron said that last night around 30 British citizens were believed to be “at risk”, but added that number has now been “quite significantly reduced”.
He said he would “continue to do everything we can to hunt the people down who are responsible for this and for other such terrorist outrages”.
Each of the families of those caught up in the crisis has been assigned a police liaison officer and is being kept fully updated of developments, he said.
BP, the joint operator of the gas plant, has also begun evacuating staff from Algeria, with 11 being flown back to London yesterday.
The Government is providing a back-up service to fill any “gaps in what BP are able to do” and all installations in Algeria have been placed on “high alert”.
US defence secretary Leon Panetta said in London today that here was “no justification for the kidnapping and murder of innocent people” in Algeria, and vowed the US government was “working around the clock to ensure the safe return of our citizens”.
Mr Cameron said the terror attck was a “well calculated” assault that is believed to have started with an attack on two buses travelling to the compound.
He told MPs: “According to the information we have from the Algerian authorities, the terrorists first attacked two buses en route to the In Amenas airfield before attacking the residential compound and the gas facility at the installation.
”It appears to have been a large, well-co-ordinated and heavily armed assault and it is probable that it had been pre-planned.
“Two of those travelling in the convoy to the airfield were, very sadly, killed, including one British national and his family were informed on Wednesday.
”A number of other workers were taken hostage by the terrorists in separate locations, both at the residential compound and the gas facility.
“The precise numbers involved remain unclear at this stage but the hostages included British nationals, along with nationals of at least seven other countries and, of course, many Algerians.”
Mr Cameron postponed a speech he was due to give in Amsterdam today on Britain's future in Europe, saying he “simply cannot be away” until the crisis is resolved.
Earlier this morning, Algerian authorities announced that there had been “some deaths and injuries” after launching their military bid to free foreign workers from Islamist militants at the plant.
Algerian security sources said that 30 hostages had died in the battle, including eight Algerians, two Britons, two Japanese and one Frenchman.
Foreign Secretary William Hague, who is cutting short a visit to Australia, told Sky News: “This remains a fluid and evolving situation and many details are still unclear, but the responsibility for the tragic events of the last two days squarely rests with terrorists who chose to attack innocent workers, murdering some and holding others hostage.
”Our priority remains at the moment to identify exactly what has happened to each British national caught up in this incident and, indeed, to help other countries determine what has happened to their nationals.“
The Algerian rescue effort was launched yesterday without consultation with the UK, to the dismay of Number 10.
Western governments are believed to have urged the Algerian authorities – in vain – to take a softly-softly approach. Algiers has a reputation for taking a violent line with hostage-taking.
Algerian communications minister Mohamed Said Belaid said the military operation succeeded in ”neutralising a large number of terrorists and freeing a large number of hostages“.
Earlier this morning a US plane landed at an airport near the In Amenas gas plant to evacuate Americans caught up in the crisis, a local source told Reuters.
Eleven or more Islamist militants were said to have died when Algerian special forces, helicopters and – according to one account – warplanes launched a series of attacks on the sprawling complex seized by an Islamist group linked to al-Qa'ida on Wednesday.
The raid on the BP complex is believed to have been inspired – and possibly led – by a veteran al-Qa'ida leader in North Africa, Mokhtar Belmokhtar. It was unclear tonight whether he was amongst the dead.
The capture of the Algerian gas site was claimed by the Islamist splinter group, Mouwaghina Bi Dam (“Those Who Sign in Blood”) as a retaliation for French intervention in Mali. But Western governments suggested that the operation must have been planned for many weeks.
The French President François Hollande said the hostage-taking in Algeria had proved France's argument that its armed intervention in Mali was about far more than the fate of the Malian government.
An unknown number of foreign captives and 600 Algerians were reported to have been freed or to have escaped from their captors during the assault.
Stephen McFaul from Belfast, was one of the lucky ones who got out. Last night he telephoned his family to say he was safe.
Mr McFaul’s family said the 36-year-old was laughing and joking as gunmen took over the plant, adding that he stayed in contact by mobile phone with his brother Brian throughout the ordeal.
”It's like riots in west Belfast,“ joked Mr McFaul, who was later discovered hiding under a bed by the terrorists.
”When news came through that Stevie was free I told mum and dad and they hugged each other, shouting at the top of their voices,“ said Brian.
One of the freed Algerian hostages told the French newspaper Le Monde that the Islamist raiders were a 20 or 30-strong multinational group from a number of countries – including a man who spoke English with a perfect British accent.
One of the dead militants was said to be a French national.
The unnamed Algerian captive said that the raiders “seemed to know the site well and knew exactly what they were looking for.… They searched the living quarters for foreigners and told Muslims that they were in no danger.”
It appeared that the gang of kidnappers had difficulty in controlling so many captives. There were reports during the day of small groups of Algerian and foreign workers escaping.
A French captive contacted by the newspaper Sud Ouest said the raiders had strapped explosives to some hostages.
The Algerian Communications Minister, Mohamed Said Belaid, claimed the rescue operation was a success. “A large number of hostages were freed and a large number of terrorists were eliminated and we regret the few dead and wounded,” he said.
According to one report, seven hostages were held for many hours after the main assault by a die-hard group of militants who resisted in part of the gas plant near the town of In Amenas, near the Libyan border.
Radio France Internationale reported from Algiers that the raiders had made four attempts to flee this morning. A convoy of buses and trucks was finally attacked from the air by the Algerian military.
The Algerians had told the raiders that they could leave the country without their hostages but the kidnappers had attempted to take some foreigners with them.
The Algerian assault came as French operations against Islamist rebels in neighbouring Mali entered a seventh day, with warplanes and helicopters continuing to pound targets in the centre and north of the country.
Despite pledges of support from a number of European nations at a meeting of EU foreign ministers, none is sending troops