Seven foreign hostages abducted in Nigeria last month by an Islamist group are believed to be dead.
The Italian and Greek foreign ministries said the hostages kidnapped from a construction firm's compound could have been killed.
Al Qaeda-affiliated group Ansaru said on Saturday it had killed the foreign hostages seized on 7 February in the northern state of Bauchi because of attempts by Nigerian and British forces to free them.
It published photos purporting to show the bodies of a Briton, an Italian, a Greek and four Lebanese workers snatched from the Lebanese firm Setraco, Reuters reports.
Britain's foreign secretary, William Hague, said a British construction worker is likely to have been killed, along with six other people of other nationalities.
Mr Hague said it was an act of cold-blooded murder that he condemned in the strongest terms.
Greece confirmed its citizen was dead, while Lebanon declined to comment.
Italy and Greece denied any attempt to rescue them had been made by any of the governments involved. Nigeria had no confirmation of the killings.
Security has become a top concern for oil and infrastructure companies across the region after gunmen loyal to al Qaeda in north Africa stormed an Algerian gas plant in January. Up to 37 foreigners died during an attempted rescue mission by Algerian forces.
The risk posed by Islamists across west and north Africa has greatly increased since France sent troops to Mail to wrest control of its northern territory from al Qaeda linked rebels.