The Algerian hostage crisis will remain the government's "top priority" until every British national at the BP gas plant is accounted for, vows Foreign Secretary William Hague.

William Hague names Algeria the UK's top priority (pic: Reuters)

According to the Reuters news agency, sixteen hostages have been freed at the plant.

Those freed included two Americans, two Germans and one Portuguese, the source told Reuters. The nationalities of the others were not immediately clear.

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.

Mr 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.

"Will remain our top priority until every British national is accounted for," the foreign secretary wrote on his Twitter feed.

"My thoughts are also with the families of everyone affected, particularly those still waiting for news of their loved ones."

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."

'Never been so relieved'

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."

Mr Strachan was interviewed on a bus alongside Darren Matthews, 29, from Teesside.

Mr Matthews said: "I am relieved to be going to see friends and family.

"I feel safe at the moment but I won't feel 100 per cent happy until I'm back in the UK, when I am back with my family.

"My heart goes out to the guys that are still there and hopefully everyone comes home safe because, at the end of the day, it's only work. No-one should have to go through that just for a job."

Read more: Algeria gas plant - a life of high risk, high reward

A Mauritanian news site reported that the remaining militants were demanding the release of two terrorists held in the United States, including 1993 World Trade Centre bombing mastermind Omar Abdel Rahman, in return for the release of two US captives.

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.