In Amenas is operated by the Algerian company Sonatrach with BP and Statoil
Two foreign nationals, one of them British, have been killed and several abducted in an attack by Islamist militants on a gas facility in eastern Algeria, state media report.
Several people were also wounded when a bus carrying workers from a gas facility near In Amenas was targeted.
After being repelled, the militants travelled to the facility, taking an unknown number of workers hostage, reports the BBC.
Militants linked to al-Qaeda claim to have been behind the incident.
They initially said they were holding six people hostage, but an alleged spokesman later told two Mauritanian news websites they were holding 41 foreigners, including US, French, British and Japanese citizens.
The Norwegian public broadcaster NRK quoted the oil company Statoil as saying there had been 17 personnel in total at the gas facility when it was taken over by the militants, 13 of whom were Norwegian nationals.
The In Amenas gas field is operated by the Algerian state oil company, Sonatrach, along with Statoil and the British oil company BP. It is about 1,300km (800 miles) south-east of the capital, Algiers, and about 60km west of the Libyan border.
The attack came after militants vowed to avenge France's military intervention in Mali, where its forces have been battling Islamists linked to Al-Qaeda in the Islamic Maghreb (AQIM) for the past week. Algeria has been allowing French aircraft to use its air space.
The Algerian interior ministry said a heavily-armed "terrorist group" using three vehicles had attacked the bus carrying workers from the In Amenas gas field at about 05:00 (04:00 GMT).
The attack was "repelled by the escort units", but one foreign national was killed and six people - two foreigners, two police and two security personnel - were wounded, a statement said.
The group then drove directly to the base and took hostage an "undetermined number of workers, including foreign nationals", the interior ministry added.
Later, the state-run APS news agency cited local officials as saying two foreigners had been killed in the attack, one of them a British national. A local source earlier told the Reuters news agency a Frenchman had died.
The Algerian military has reportedly launched an operation to rescue the hostages and surrounded the gas workers' camp at Tiguentourine.