A British man is "likely to have been killed" at the hands of his captors in Nigeria in an "act of cold-blooded murder", Foreign Secretary William Hague said today.
The construction worker, who had been held hostage since February 16, is believed to have been killed alongside six other foreign nationals.
In a statement, Hague said: "It is with deep sadness that I must confirm that a British construction worker, held hostage in Nigeria since 16 February, is likely to have been killed at the hands of his captors, along with six other foreign nationals who we believe were also tragically murdered.
"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.
"I ask the media to allow them time to come to terms with their loss in privacy.
"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 the extremist group, identified as Ansaru, was published online and could not be immediately verified.
It said Ansaru members killed the hostages after British warplanes were reported to have been seen in the northern Nigeria city of Bauchi by local journalists.
In a statement, the group said: "As a result of this operation, the seven hostages were killed."
On that matter, the British Foreign Office said today: "There are a number of deployments as parts of various engagements in Africa which will include the movement of assets."
This is not the first time hostages have been killed in Nigeria.
British national Chris McManus and Italian co-worker Franco Lamolinara died in a failed rescue bid in March last year as Nigerian troops and UK Special Boat Service commandos tried to end their nine months in captivity.