News agencies report that five Japanese nationals and a French citizen were taken by Islamic militants from the town of In Amenas.

The oil giant BP operates a production facility in the town and it said there had been an incident but did not confirm the kidnapping.

British diplomats said they were aware of "a terrorist incident".

A spokesman said it "was seeking clarification from oil companies working in the area as to whether they have personnel involved in the incident."

But French and Algerian officials were unable to confirm the abduction. Japan is making inquiries.

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.

The abduction comes as French forces are preparing to attack Islamist militants in Algeria's southern neighbour, Mali.