The BBC's Brian Hanrahan: "Yemeni police blame a radical group"

Details are still not clear but it is believed that four British travellers - two men and two women - died in the incident in Yemen's southern province of Abyan.

The four were among a party of 16 Western tourists - 12 Britons, two Americans and two Australians - who were travelling with the British-based tour operators Explore Worldwide. They were abducted on Monday despite a police escort.

Brian Hanrahan: "A tougher approach to kidnapping"

Two of the kidnappers are also believed to have been killed by the Yemeni security forces. Four others have been arrested and face the death penalty under legislation introduced in the summer in a bid to stamp out kidnapping in the Yemen.

Yemeni officials say the security forces intervened when the kidnappers began killing their captives.

Botched rescue

BBC Correspondent Frank Gardner: "This is a black day for the Yemen"

But our correspondent says a source close to Yemen's President Ali Saleh told him the casualties were the unfortunate result of a planned operation to free the hostages. He says it appears to have been a massive "botch-up".

He says it appears the Yemeni authorities were unwilling to discuss the kidnappers' demands, which included the release of the leader of an Islamist group.

Yemen is advertised as the "Land of Sheba" in Explore's brochures

Correspondents say Yemeni tribesmen frequently use kidnappings to press their demands for improved health and social services in tribal areas.

Germans still missing

Four German tourists abducted three weeks ago are still being held in the eastern province of Marib.

In the past, the government has caved in to economic demands made by abductors - who have kidnapped about 100 foreigners in the past six years - but he says this incident appears to bring an end to the "era of benign kidnappings".

The tourists were travelling with the UK-based company, Explore Worldwide, in conjunction with a Yemeni holiday firm.

Explore Worldwide spokeswoman Sue Ockwell: "All trips to Yemen are on hold"

A spokesman for Explore Worldwide, who are based in Aldershot, Hampshire, said all trips to Yemen were on hold while their operations were "under review".

Unlike Chechnya, Yemen is not on a list of countries which the British Foreign Office advises tourists against visiting on any account.

The Foreign Office says: "British visitors and residents in Yemen should be aware of a risk of random kidnapping throughout the country including the capital Sana'a."