The Algerian government says 32 fighters and 23 captives have been killed during a three-day military operation to end the hostage crisis at a natural gas plant in the Sahara.
The provisional death toll was issued by the Algerian interior ministry on Saturday after a special forces operation crushed the last holdout of the fighters at the In Amenas plant, resulting in 11 captors killed along with seven hostages.
A total of 685 Algerian and 107 expatriate workers were freed over the course of the operation, which began on Wednesday, a ministry statement said.
"The hostage situation has been brought to an end by a further assault by Algerian forces which has resulted in further loss of life," Philip Hammond, UK defence secretary, said at a joint news conference with his US counterpart, Leon Panetta, in London.
"We're pressing the Algerians for details on the exact situation."
He said that the loss of life was "appalling and unacceptable and we must be clear that it is the terrorists who bear sole responsibility for it".
British nationals dead
Later William Hague, UK foreign secretary, said five British nationals and a British resident were dead or unaccounted for in the hostage crisis.
The Amenas gas plant is jointly operated by British firm BP and Algeria's state-owned Sonatrach.
BP said on Saturday that 14 of its 18 employees at the gas complex were safe but the fate of the remaining four remained unknown.
A Japanese engineering firm said on Sunday that 10 of its Japanese and seven of its foreign workers remained unaccounted for, adding the situation was "grave".
The Malaysian foreign ministry, quoting the firm, JGC Corp., said that two of its nationals were among the seven unaccounted for, and there was a "worrying possibility" that one of them was dead.
The other three Malaysians who had been working at the plant had been confirmed safe.
Al Jazeera's Paul Brennan reports on the deadly end of the Algerian hostage crisis in the Sahara
Those freed on Saturday included two Americans, two Germans and one Portuguese, sources told Reuters news agency.
France has refrained from criticising the military action that claimed one of its countrymen among the fallen in the former French colony.
Francois Hollande, the French president, said the Algerian action was appropriate in the face of "coldly determined terrorists".
"When there is a hostage-taking with so many people involved and such coldly determined terrorists, ready to kill their hostages - which they did - a country such as Algeria has had ... the most appropriate responses because there could be no negotiations," Hollande said in Tulle, southcentral France.
The French air force requires access to Algerian airspace for its bombing campaign in neighbouring Mali.
Other nations have criticised the action, with Britain, Japan and Norway insisting they should have been forewarned of the first army assault on Thursday.
Algeria's response to the crisis was typical of its history in confronting fighters, favouring military action over negotiation, which caused an international outcry from countries worried about their citizens.
Military forces twice assaulted the two areas where the hostages were being held with minimal apparent mediation.
A spokesman for the captors, known as Signatories in Blood, told Al Jazeera earlier on Saturday that they were still open to negotiations regarding a prisoner swap with the Algerian military.
'Heavily armed' captors
APS, the Algerian state news agency, earlier quoted a government official as saying that the captors, who claimed to have come from Niger, were heavily armed with machine guns, assault rifles, rocket launchers and missiles.
The interior ministry said the captors consisted of 32 men of various nationalities, including three Algerians.
The crisis began on Wednesday when al-Qaeda-linked fighters attacked the bus carrying 19 foreigners working at the gas complex to the nearby airport.
The men seized the plant to avenge what they said was the country's support for French military action in neighbouring Mali.
Some of those who escaped said explosives had been wrapped around their necks and others said they hid, petrified, wherever they could.
The Algerian interior ministry said the army managed to recover a weapons cache that included six machine guns, 21 rifles, two 60mm mortars, two RPG rocket launchers, and 10 grenades fitted in belts, as well as as ammunition and explosives.