The UK today condemned al Qaida's "barbaric" murder of a British man kidnapped in Mali over four months ago.
Edwin Dyer was one of four European tourists taken hostage on January 22 as they returned from a cultural festival.
They were held by the terror movement's North African wing, known as Al Qaida in the Islamic Maghreb (AQIM).
Despite intense behind-the-scenes negotiations by UK and local officials, the hostage-takers claimed today that they had carried out their threat to kill Mr Dyer.
Prime Minister Gordon Brown said there was "strong reason" to believe this was true.
He said: "I utterly condemn this appalling and barbaric act of terrorism. My thoughts are with Edwin Dyer's family. I offer them the condolences of the whole country."
Mr Dyer, who had been working in Austria and spoke fluent German, was on holiday in West Africa with German travel operator Oase Reisen.
He was abducted, along with a Swiss couple and a German woman, near the border with Niger after attending a festival of nomad culture at Anderamboukane in Mali.
At first it was believed that the hostage-takers were Tuareg rebels, who have regularly clashed with Mali's army, but in February AQIM claimed responsibility.
Two of the captives were released in mid-April but days later the terrorists issued an ultimatum, warning they would kill Mr Dyer unless the UK freed radical cleric Abu Qatada within 20 days.
The deadline was extended by 15 days to May 30, but in the end frantic efforts to secure the safe release of the Briton failed.
In a statement issued today AQIM said: "The British captive was killed so that he, and with him the British state, may taste a tiny portion of what innocent Muslims taste every day at the hands of the Crusader and Jewish coalition to the east and to the west."
Mr Brown said: "This tragedy reinforces our commitment to confront terrorism.
"It strengthens our determination never to concede to the demands of terrorists, nor to pay ransoms.
"I want those who would use terror against British citizens to know beyond doubt that we and our allies will pursue them relentlessly, and that they will meet the justice they deserve.
"I have regularly discussed this case with the President of Mali - he knows that he will have every support in rooting out al Qaida from his country."
Foreign Secretary David Miliband pledged that Britain would continue working to secure the release of the Swiss man still being held by the group.
He said: "Hostage-taking and murder can never be justified whatever the cause. This tragic news is despite the strenuous efforts of the UK team in the UK and Mali, with valuable help from international partners."
Qatada is currently being held in prison in the UK as he fights a bid to extradite him to Jordan, where he faces terror charges.
The Law Lords ruled in February that he can be deported, but his lawyers are appealing against the verdict, claiming he faces torture if he is returned to the Middle East country.
He was first arrested in the wake of the September 11 2001 attacks on America and has been described as "al Qaida's spiritual leader in Europe".