The Foreign Office has said it is "urgently investigating" claims from a breakaway Islamist group that they have killed a British national in Nigeria.
In a statement released on an Islamist website, the Ansaru group said it had killed the hostages in response to attempts by Britain and Nigeria to free them, SITE Monitoring Service reported.
Ansaru is one of several Islamist groups that have become the main security threat in Nigeria, Africa's largest oil producer. The al-Qa'ida-aligned group blasted into the compound of Setraco, a Lebanese construction company, on 7 February, abducting a Briton, an Italian, a Greek and four Lebanese workers.
A Foreign Office spokesman said: "We are aware of reports of the death of a British national in Nigeria and are urgently investigating."
The statement issued in Arabic and English on an affiliate of the Sinam al-Islam network was accompanied by screen shots of a video purporting to show the dead hostages, SITE said.
One shot (above) showed a man with gun standing above several figures lying on the ground. The image was not clear enough to see if they were dead or much detail about them.
The hostage-taking, in the remote town of Jama'are in Bauchi state, was the biggest number of foreigners seized in the mostly Muslim north since the Islamist insurgency there intensified two years ago.
But Nigerian officials doubt whether the killing has even happened, with Bauchi Police Commissioner telling Reuters: "As far as I'm concerned, and to the best of my knowledge, nothing like that has happened."
Lebanese and Italian officials said they were checking the reports, and Mohammed Abdullah, a spokesman for Setraco, also said he had heard nothing about any harm done to the hostages.