Italy and Greece have acknowledged that seven foreign hostages kidnapped in northern Nigeria last month were killed as claimed by Islamist militants.
British Foreign Secretary William Hague Sunday called it "an act of cold-blooded murder" and condemned it "in the strongest terms." He said it was "likely" the Briton was killed along with the six others.
Four Lebanese citizens, and one each from Britain, Greece and Italy, were taken from Nigeria's northern Bauchi state on February 16. All seven were employees of Setraco, a Lebanese construction company with an operation there.
Italy and Britain said the hostages were killed by the al-Qaida-affiliated group known as Ansaru. Greece also confirmed one of its citizens was killed, while Lebanese authorities did not immediately comment.
On Saturday, Ansaru issued a communique saying it had killed the hostages in part because of attempts by Nigerian and British forces to free them. The group published grainy photos along with the statement that purportedly showed the bodies of all seven victims.
Greece and Italy have both denied the claim that any government forces attempted to free the hostages.
Ansaru also blamed the killings on a pledge by Nigerian President Goodluck Jonathan to do "everything possible" to free the captives. Nigerian authorities have yet comment publicly on Ansaru's claim.
In January, Ansaru declared itself a splinter group independent from Boko Haram, northern Nigeria's main terrorist organization.
Boko Haram - which means "Western education is sacrilege" - has conducted a guerrilla campaign of bombings and shootings across the country's predominantly Muslim north. Islamist groups operate throughout the region.
Nigeria is Africa's most populous nation and largest oil producer.