A British construction worker held hostage in Nigeria since 16 February “is likely to have been killed” by his captors, Foreign Secretary William Hague has said.
The man, who has not been named, is one of seven foreign nationals thought to have been killed.
Mr Hague condemned the killings as “an act of cold-blooded murder”.
The hostages were captured in a raid on a construction site in the northern state of Bauchi.
Mr Hague said in a statement it was “with deep sadness” that he must confirm the Briton was “likely to have been killed at the hands of his captors, along with six other foreign nationals who we believe were also tragically murdered”.
He added: “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 said responsibility “for this tragic outcome rests squarely with the terrorists”.
Britain would work with the Nigerian government “to hold the perpetrators of this heinous act to account”, Mr Hague added.
The other hostages were from Lebanon, Greece and Italy.