The evidence increasingly suggests that the four Britons and one French citizen, who were on the staff of Britain's Embassy in Addis Ababa, were abducted by tribal rebels in the remote Danakil Depression rather than by terrorists with an anti-Western agenda.

After being taken from the settlement of Hamedela in the northern province of Afar, reports suggest they were led across the border into Eritrea.

British sources believe that separatist insurgents from the local Afar tribe - who regularly move through Eritrean territory - probably captured the embassy party.

The Afar live on either side of the bitterly disputed border between Ethiopia and Eritrea.

Tribal leaders are thought to be helping with the search. They have passed on eyewitness accounts that the captives are alive and well.

Seyoum Mesfin, Ethiopia's foreign minister and one of the most powerful figures in the government, gave an optimistic assessment.

"They will be freed alive very soon," he told the Sub-Saharan Informer newspaper. "Right now, I can't say we are doing this or that, but we are doing something."

In another interview, Mr Seyoum said: "I heard they are safe and secure. They are in good condition. We don't even know yet who the kidnappers are."

Mr Seyoum hinted that Ethiopia knew where the captives were being held but added: "We cannot disclose the place where they are because we believe that this will endanger their safety."

Other Ethiopian officials have been more specific. Ali Din, the police commissioner for the Afar region, told state radio that the captives were being held in a military camp in the Eritrean town of Weima. They were kidnapped about 30 miles from the frontier.

Two Ethiopians who were taken alongside the embassy party and later released told The Daily Telegraph that the hostages were led northwards, towards the border with Eritrea.

A British spokesman in Ethiopia was unable to confirm any of these reports but said they were all being investigated.

A team of British officials has arrived in Ethiopia's northern town of Mekele, the nearest administrative centre to where the abductions took place.

A small rebel group styling itself the Afar Revolutionary Democratic Front has been operating in the Danakil desert for many years.

Their aim is to carve out a united and independent Afar state. By kidnapping foreigners, they could deal a severe blow to Ethiopia's tourist industry, a growing sector to which the government attaches a high priority.