An al-Qaida-affiliated group operating in Mali says it has executed a British hostage because Britain failed to release an imprisoned radical cleric.

The group, which calls itself al-Qaida in the Islamic Maghreb, posted a message on the Internet saying it killed Edwin Dyer on May 31.

Britain's Prime Minister Gordon Brown condemned the apparent execution of Dyer as "appalling and barbaric." 

Mr. Brown said he has discussed the case with Mali's president, Amadou Toumani Toure, and promised to work with allies to pursue those who use terror against British citizens.

The al-Qaida group had demanded that Britain release Jordanian cleric Abu Qatada.  British authorities arrested Qatada in 2002 and claim that he is al-Qaida leader Osama bin Laden's top European deputy.

The British man was one of six Westerners who were kidnapped in December and January along the border of Mali and Niger. 

Two European tourists and two Canadian diplomats were later released, leaving Dyer and a Swiss citizen in captivity.

The Swiss Foreign Ministry condemned Dyer's killing and is calling for the release of the Swiss hostage.

The al-Qaida group, once known as the Salafist Group for Preaching and Combat, is believed to have held the hostages in northern Mali.