The Algerian Press Service (APS) reported that ‘‘a little more than 20’’ foreign workers were seized at the In Amenas gas field on the Algerian border with Libya, although earlier reports put the total number of hostages at 41.

The group was  reported to include Norwegians, Americans, British, Irish, French and Japanese nationals. Algerian workers at the gas field - a joint venture between BP, the Norwegian oil company Statoil, and the Algerian state oil firm, Sonatrach, with a Japanese firm, JGC Corp, providing services - were released by the hostage-takers soon after the attack.

There were unconfirmed reports that the militants had rigged the site with mines or other explosives.

The Norwegian government confirmed that the hostages were being held within the natural gas facility. The country’s foreign minister, Espen Barth Eide, said: ‘‘We’ve asked the Algerian authorities to put the life and health of the hostages above all.’’

There were claims of responsibility from groups calling themselves the Masked Brigade and Signers in Blood, both names used by followers of a former al-Qaeda in the Islamic Maghreb leader called Mokhtar Belmokhtar. They said the attack was a reprisal for the French intervention in Mali, Operation Serval, which Algeria has supported by opening its air space to French warplanes.

Belmokhtar, a veteran of Algeria’s civil war and of the Soviet invasion of Afghanistan, was a deputy commander of al-Qaeda in the Islamic Maghreb until last month, when he broke away and set up his own group.

Guardian News & Media