Seven foreign hostages kidnapped by a Nigerian Islamist group from a construction firm compound last month have been killed.
Ansaru, which is affiliated with al-Qaeda, said it had killed the hostages seized on 7 February in the northern sate of Bauchi because of attempts by Nigerian and British forces to free them.
It published grainy photos alongside the statement, purporting to show the bodies of a Briton, an Italian, a Greek and four Lebanese workers snatched from the Lebanese firm Setraco.
An armed militant stood in front of them.
Nigerian authorities said they had no information on the killings, and they doubted the veracity of the group's statement.
However, Britain's Foreign Secretary William Hague condemned the apparent "cold-blooded murder" of a British hostage and six other nationals.
The Briton was named as construction worker Brendan Vaughan.
An Italian Foreign Ministry statement said: "Our checks conducted in co-ordination with the other countries concerned lead us to believe that the news of the killing of the hostages seized last month is true."
The Greek Foreign Ministry said: "The information we have shows that the Greek citizen is dead," adding, the ministry had informed his family.
The Greeks and Italians both said there had been no attempt by any government forces to free them.
Islamist groups operate throughout the north of Africa's top oil producer, where they have become the main security threat to it after an amnesty ended an uprising by armed groups in the oil-producing southeastern Niger Delta region.
Kidnappings have been rife in the southeast for many years, but the gangs there usually seek a payout and hostages tend to be released quickly, while Islamist kidnappings in the north are often fatal.