Meanwhile the authorities in Asmara, Eritrea's capital, have strongly denied charges by Ethiopian officials that its soldiers were responsible for last week's abduction and the Addis Ababa government has not repeated the accusation.
Gebremarian Hadush, a local army commander, also blamed Eritrea and said the hostages were being held in Wiema on the other side of the frontier.
He said Afar separatists based in Eritrea might also be involved: "They work together with the Eritreans. They must have done this together," he said.
Asked if the military were preparing a rescue mission, he replied: "That is in the hands of the federal government. We will take that measure if it is an order."
A three-member British investigation team left the kidnap area on Tuesday but there was no sign it had made progress.
The team did not comment as it left Berahile, a town of sandy streets that Ethiopian police are using as a staging area.
The five hostages, who include diplomats and other people linked to the British embassy in Addis Ababa, are believed to have been kidnapped about 50 km away in Hamad-Ile.
Investigators on Monday found two of their vehicles abandoned there, riddled by shrapnel.
Police in the town, where trains of camels hauling loads of salt blocks ply rough tracks, declined to give more details of the investigation on national security grounds.
"Our teams are out there. We are doing everything we can," said one police officer who declined to give his name.
A foreign office spokeswoman in the Ethiopian capital said: "The discovery of the vehicles has been very distressing for the families of the missing people. We want to stress that we have no reason to believe that the people were in the vehicles."
Inhabitants of Hamad-Ile said about 50 men in Eritrean uniforms grabbed the hostages and then threw a hand grenade to disable their vehicles and prevent pursuit.
Witnesses said some of the Europeans' personal belongings remained in the vehicles, suggesting robbery was not the motive.
The British investigating team comprised Deborah Fisher, the deputy British ambassador, a forensics expert and a third official that believed to be a special forces officer.
The British government does not comment on special forces operations, but is known to have hostage rescue teams that include elite soldiers.
No one has claimed responsibility for the kidnapping, or demanded ransom.
Afar is home to one of the world's hottest and driest climates, where the nomadic Afar people roam in barren landscapes of mountains and dry riverbeds in temperatures that often reaching 45 degrees Celsius.
Tourists, who usually travel with armed guards to protect them from bandits, brave the climate to see ancient salt mines, volcanoes and the part of the Danakil Depression - one of Africa's lowest areas - which runs through Afar.