Foreign Secretary William Hague has condemned "in the strongest terms" the apparent "cold-blooded murder" of a British hostage and six other foreign nationals at the hands of captors in Nigeria.
Mr Hague said his thoughts were with the loved ones of the Briton, who he named as construction worker Brendan Vaughan.
Mr Hague said in a statement: "This was an act of cold-blooded murder, which I condemn in the strongest terms.
"My thoughts are with his family, and the families of the other hostages, who will be devastated by this tragic loss. I offer them our deep condolences at this terrible time, and know that the thoughts of people up and down our country will be with them."
He added: "Responsibility for this tragic outcome rests squarely with the terrorists. I am grateful to the Nigerian Government for their unstinting help and co-operation.
"We are utterly determined to work with them to hold the perpetrators of this heinous act to account, and to combat the terrorism which so blights the lives of people in Northern Nigeria and in the wider region."
Those kidnapped included three Lebanese citizens and one each from Britain, Greece, Italy and the Philippines - all employees of Setraco, a Lebanese construction company with an operation in Bauchi state, local officials said at the time.
The news comes a day after a message from Ansaru, the extremist group behind the kidnappings, which said the hostages were killed after British warplanes were reported to have been seen in the northern Nigerian city of Bauchi by local journalists.
In a statement, the group said: "As a result of this operation, the seven hostages were killed."
Commenting on the claim, the Foreign Office said: "There are a number of deployments as parts of various engagements in Africa which will include the movement of assets."