British hostage Edwin Dyer was killed by al-Qaeda militants in Mali, British Prime Minister Gordon Brown said Wednesday. (IntelCenter/Associated Press)

The British prime minister says he has "strong reason to believe" a Briton captured in Mali has been killed by al-Qaeda militants.

Edwin Dyer was travelling in Niger on January 22 when he was captured along with three other European tourists, but had been reported to be held in Mali.

Al-Qaeda in Islamic North Africa, known by the French acronym AQMI, released two captives, both women, in April. The fate of the other hostage, a Swiss man, remains unknown.

"We have strong reason to believe that a British citizen, Edwin Dyer, has been murdered by an al-Qaeda cell in Mali," Brown said in a statement. "I utterly condemn this appalling and barbaric act of terrorism."

It is unclear what evidence there was of Dyer's killing.

But the SITE intelligence group, a Washington-based firm that monitors militant messages, posted a purported AQMI statement on Wednesday in which the group claimed responsibility for the killing.

The notice said Dyer was executed on Sunday, although it is unclear how he was killed. The posting was not accompanied by a photo or video to verify the claim, and its authenticity could not be immediately verified.

No ransom

Dyer's captors had threatened to kill him if Britain refused to release Abu Qatada, a hardline cleric.

Qatada, who remains in jail, has been described in Spanish and British courts as a leading al-Qaeda figure in Europe.

"This tragedy reinforces our commitment to confront terrorism. It strengthens our determination never to concede to the demands of terrorists, nor to pay ransoms," Brown said.

Dyer, who had recently worked in Austria and was fluent in German, was touring a nomad festival in Niger along with a number of other European tourists when he was kidnapped.

The Swiss government swiftly condemned the killing, and called for the immediate release of the Swiss hostage. The man's wife, who was also taken hostage by the militants, was released in April.

"Our thoughts are with the grieving relatives in Great Britain and the relatives of the Swiss hostage who continue to hope with all their hearts for the speedy release and return of their loved one," the Swiss foreign department said in a statement.

No compromise

In the statement posted on the internet, AQMI said it was talking with a British negotiator about the release of Dyer, and had agreed to extend an initial deadline for Abu Qatada's release. But the talks stalled after there appeared to be no compromise, the group said.

AQMI is an Algeria-based group that joined Osama bin Laden's terrorist network in 2006. It operates mainly in Algeria, but is suspected of crossing the country's porous desert borders to spread violence in the rest of northwestern Africa.

In April, AQMI freed four foreign hostages in Mali, among them Canadian diplomats Robert Fowler and Louis Guay.

Abu Qatada, a Palestinian-Jordanian, arrived in Britain in 1993. He has been in jail almost continually since 2002, accused of advising militants and raising money for terror attacks. In 2005, Britain ordered him deported to Jordan where, in his absence, he had been sentenced to life for conspiracy to commit terrorist activities.

He has been fighting his extradition.

With files from The Associated Press