Al-Qaida terrorists have killed a Briton taken hostage in Mali, the British prime minister said Wednesday. The fate of a Swiss hostage taken at the same time was unknown. A statement issued in the name of al-Qaida on an Internet site frequently used for extremist messages said the captive, Edwin Dyer, was killed on Sunday. Dyer was abducted in January and his captors in Mali had threatened to kill him by the end of May if Britain refused to release extremist preacher Abu Qatada from prison. Qatada, who remains in jail, has been described in Spanish and British courts as a leading al-Qaida figure in Europe. "We have strong reason to believe that a British citizen, Edwin Dyer, has been murdered by an al-Qaida cell in Mali," British Prime Minister Gordon Brown said in a statement issued by his office. "I utterly condemn this appalling and barbaric act of terrorism." Officials said that Dyer was thought to be in his late 50s or early 60s and had recently lived in Austria. The message posted on the Internet had no video or photo to back up the claim and its authenticity could not be independently verified. But the SITE intelligence group, a Washington-based firm that monitors militant messages, also reported the statement on Wednesday. "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. The Swiss government also condemned the killing and called for the immediate release of a Swiss hostage captured at the same time as Dyer. The man has been identified by Swiss media as Werner Greiner. His wife, Gabriella Barco Greiner, was released by the hostage-takers in April. "Hostage-taking and murder can never be justified whatever the cause," Britain's Foreign Secretary David Miliband said. He said British officials are working to help secure the release of the Swiss hostage. Kidnappers holding Dyer said in April that they would execute him if the cleric wasn't freed by the end of May. 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 is appealing to the European Court of Human Rights to overturn the decision to deport him. In the statement, attributed to Al-Qaida in Islamic North Africa - known by the French language acronym AQMI - the kidnappers claimed Dyer was killed on Sunday. "The British state was made to taste a very small part of what innocent Muslims taste every day at the hands of the Crusader and Jewish coalition," the group said in the statement, according to a transcript prepared by SITE. The group said it had agreed to extend an initial deadline for Abu Qatada's release following discussions with a British negotiator, but indicated further talks had failed to reach any compromise. 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. Last month, AQMI kidnappers in Mali freed four foreign hostages, including two UN officials.