Islamist militants in Algeria say they have taken up to 41 foreigners hostage, including seven Americans, in an attack on a natural gas field.

The militants tell regional media the raid early Wednesday was in retaliation for France's military intervention in Mali.

The attackers reportedly have killed two people, including a British national, and wounded at least six others.

The gas field is partly operated by British energy company BP, which confirmed via Twitter that a “serious security incident” was in progress at its Ain Amenas gas facility.

The British Foreign Office said British nationals are “caught up” in the incident, while U.S. defense officials say they are in contact with military forces in the region.

After the facility's seizure, Algerian forces surrounded the kidnappers. Negotiations for the release of the hostages, who also include Norweigian and Japanese nationals, are ongoing.

BP operates the facility along with the Norwegian company Statoil and the Algerian state oil company. A Japanese company provides services.

French military forces entered Mali on Friday to help drive back Islamist militants pushing south, in the direction of the capital.

The Islamist groups that control northern Mali include al-Qaida in the Islamic Maghreb and two others believed to have links to al-Qaida.

Algeria had long warned against military intervention against the rebels in northern Mali, fearing the violence could spill over its own long and porous border.