A man from Northern Ireland travelling on an Irish passport is among several foreigners abducted by Islamist militants in eastern Algeria.
Algerian security officials say one person was killed and others abducted in an attack on a gas facility at In Amenas in the east of the country.
Islamist militants allied to Al-Qaeda say they carried out the attack.
Ireland's deputy prime minister Eamon Gilmore has called for the man's immediate release.
"The government stands ready to use all the resources available to us to ensure that our citizen is released as soon as possible," he said.
"I would ask that the family be allowed privacy at this difficult time."
The Department of Foreign Affairs said it was providing consular assistance to the family and was in close contact with its international partners and a wide range of other contacts in order to establish the facts of the situation.
The oil giant BP says a gas field it runs in partnership with Norwegians and Algerians was attacked.
The British Foreign Office confirms its nationals have been working in the area where a "terrorist incident is ongoing". But a spokesperson could not say whether British staff had been abducted.
A Japanese contractor at the In Amenas field, JGC Corp, says Japanese staff have been seized, according to Japanese media.
Early reports said five Japanese nationals and a Frenchman had been seized, but a Western diplomat told the French news agency AFP those abducted included British and Norwegian staff.
The Algerian army has begun an operation to recover the hostages.
The In Amenas gas field is a joint operation by BP, the Algerian state oil company, Sonatrach, and the Norwegian state energy firm, Statoil.
The attack comes as French ground forces are preparing to engage Islamist militants in Algeria's southern neighbour, Mali.
Algeria has been allowing French aircraft to use its air space to attack targets in Mali.
The militants, who called themselves the Khaled Abul Abbas Brigade, said they had travelled from northern Mali to launch the attack.
Islamist militants in the region have in recent years seized a number of foreigners, mainly in Mali. Eight French nationals are currently being held across the region.