Nigerian Islamist group Ansaru says it has killed seven foreign hostages abducted from a construction site to the north of the country last month.

However authorities and the construction company itself, Setraco, have yet to confirm the news.

A group, considered a splinter faction of Islamist extremist group Boko Haram, has issued a statement and photographs purporting to show the dead hostages.

Last month Nigeroam police said four Lebanese, one Briton, a Greek citizen and an Italian were among the kidnapped.