The Algerian hostage crisis will remain the Government's "top priority" until every British national at the BP gas plant is accounted for, Foreign Secretary William Hague vowed on Saturday.
Around ten UK workers at the remote desert complex are thought still to be "at risk" as Algerian special forces continue to hunt the site for the remaining terrorists.
The Algerian state news agency APS reported that 12 foreign and Algerian workers and 18 Islamist militants had been killed in fighting after troops stormed the plant at In Amenas on Thursday.
Details remain sketchy but the figures suggest that around a dozen of the original group of 30 heavily armed terrorists could still be holed up at the complex - possibly still holding hostages.
Hague, who returned early from a visit to Australia, was due to chair a meeting of the Government's Cobra emergencies committee, as officials in Whitehall continued to monitor developments closely.
The Foreign Secretary wrote on Twitter:
APS reported that around 100 of the 132 foreign workers at the site had been freed along with 573 locally employed staff.
One of the men held hostage, Iain Strachan, 38, from Howwood in Renfrewshire, spoke to an Algerian television channel about his ordeal.
He said was "very relieved to be out", adding: "Obviously we still don't really know what's happening back on site.
"So, as much as we're glad to be out, our thoughts are with colleagues who are still there at the moment."
He said the Algerian army's assistance has been "fantastic".
"I've never been so relieved as when they came and got us off site," he said.
"We thank them very much for that."
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, the source added, 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".