Three British officials were among 15 Western tourists being held yesterday by kidnappers in a remote corner of Ethiopia dubbed the "land of death" because of its extreme climate.
The Britons, who have links to the British embassy in the Ethiopian capital, Addis Ababa, were in one of two convoys intercepted on Wednesday in the barren Afar region close to the border with Eritrea roamed by separatist rebels and bandits.
Whitehall sources said last night that there was a "national security dimension" to the kidnappings and that the government's emergency committee, Cobra, had met over the incident.
The second group, comprising ten French citizens, was believed to be being held by the same kidnap gang after both convoys were stopped in the Danakil Depression, a spectacular desert bowl that contains the lowest point in Africa more than 500 metres below sea level.
There were unconfirmed reports last night that the French group, who may have been held at a different location from the Britons, had been released unharmed.
The Foreign Office said it was investigating the disappearance of the Britons but said details remained sketchy about the circumstances of how they were taken.
Under Ethiopian government rules for tourists, all groups of visitors to Afar, in the north east of the country, have to be accompanied by at least two armed guards.
A FCO spokesman said: "We are urgently investigating the disappearance and reports that a number of tourists have subsequently been found."
Whitehall sources underlined that situation was uncertain and potentially perilous for any hostages.
Dalol, the village where the kidnappings took place, is on the border with Eritrea, which has a fraught relationship with Ethiopia.
The border is frequently the scene of clashes between armed groups and security forces.
One of those kidnapped was named as Rossanna Moore, the Italian-born wife of Michael Moore, the director of the British Council in Addis Ababa, which deals with cultural relations.
The others are thought to be middle-ranking officials with the diplomatic service and the Department for International Development.
The British group was on a long-planned trekking trip to ancient and spectacular salt mines in Dalol, which have become an increasing attraction for intrepid travellers in recent years.
Several tour organisations have sprung up offering guided visits to the Danakil Depression in off-road vehicles.
The region, which is of huge geological and archaeological significance after three-million-year-old fossils of early human remains were found in the area, is one of the most hostile environments on the planet.
The average temperature is 34C and the daytime heat can often reach 45C.
It is often wracked by volcanic eruptions and earth tremors.
The renowned 20th century British explorer Wilfred Thesiger described it as a "veritable land of death".
It was unclear whether the tourists had fallen foul of a kidnap group with criminal motives or Afar separatists who have been fighting a low-level campaign against the Ethiopian government for an autonomous state straddling territory in Ethiopia, Eritrea and Djibouti.
The two groups are thought to have travelled on Sunday by road to Makele, the principal town in Afar, some 500 miles north east of Addis Ababa.
They then travelled with their tour agency, Origins Ethiopia, to Hamedali, a remote village that was to act as a base for their visit.
Each group was travelling in two off-road vehicles, accompanied by a guide, a cook and two armed guards.
According to reports, one of the tourists in the French group managed to escape the kidnappers and flagged down another tourist party before using a satellite phone to alert the authorities.
Stephane Gompertz, the French ambassador in Addis Ababa, said: "A kidnapping or kidnappings did take place. It seems that the incident or incidents happened two days ago in the evening. At the moment, we don't know which group may be involved or why they have done this."
There have been kidnappings in the region before.
In 1995, rebels from the Afar Revolutionary Democratic Unity Front claimed responsibility for holding two Italian tourists.
They were released unharmed after two weeks.
The crisis is a blow to attempts by the Ethiopian government to boost tourism.
The country's tourism minister said Addis Ababa wanted to make Ethiopia one of Africa's top ten tourist destinations by 2020 with more than one million visitors a year.
It currently receives 250,000 foreign tourists a year.
One British-based tour operator said: "It is a tragedy for the Afar people because tourism which provides vital income was just beginning.
Hopefully, this is just a row which has got out of hand between guides and the locals but of course it could be something more sinister."The Foreign Office said yesterday it had changed its travel advice for Ethiopia in the light of the kidnapping and was advising against all travel to Afar.