British rescuers in Iran have not given up hope of finding earthquake survivors despite recovering only bodies so far.
But the leader of the Rapid-UK search team admits the chances of finding people alive in the ruins of Bam are dropping with each passing hour.
More than 60 UK doctors, paramedics and volunteers have joined emergency workers in the city where at least 10,000 are feared dead.
The charity's John Holland said the team had checked 18 buildings so far.
Mr Holland, speaking from the 20-strong team's makeshift base on a football pitch in the heart of Bam, said the earthquake had virtually destroyed the historic city.
He said: "We have not found any survivors - but we have found quite a few bodies.
"In this type of situation the chances of finding someone alive are quite low, to be honest. As more time goes on, obviously the chances dramatically lower."
But he said it was too early to give up all hope and cited the discovery of an 11-year-old boy by a Rapid-UK search team amid the wreckage of the Gujarat earthquake in India after 84 hours.
The British Embassy in Tehran said that a Briton who was in the area is missing, while another UK national was slightly injured in the earthquake.
A further 28 Britons known to be in Bam, one of Iran's most important tourist sites, escaped the earthquake unhurt.
The UK Government has pledged £150,000 to help pay for emergency supplies.
British rescuers flew from Stansted Airport in Essex to Kerman, 125 miles from the epicentre of Friday's quake, which also injured thousands of people and destroyed around 70% of homes.
Rapid-UK's team have been sifting through rubble from 18 buildings so far, including schools and hospitals.
They have specialist equipment with them, including snake-eye cameras, high-tech listening devices and carbon dioxide detectors, to search for people trapped under buildings.
Members of the International Rescue Corps (IRC), sniffer dogs, and fire and rescue teams from Essex, Hampshire and Kent also flew out to assist in the search operation.
Rescue specialist Paul Worcester said their dogs, which had been working "flat out", were getting tired.
He said the team would continue to work round the clock for the next 24 hours in the hope of getting someone out alive.
The British Red Cross (BRC) has launched an appeal to raise money for tents, tarpaulins, water containers, kitchen sets and water purification tablets.
Its team will co-ordinate the international relief effort, directing aid as it arrives in Iran.
Spokesman Mike Goodhand said after the initial search and rescue effort ended, a relief phase would be entered to help those who survived.
He estimated the Red Cross would stay in the area for a further two to three years "helping people rebuild their lives".
International Development Secretary Hilary Benn described the earthquake as a "major catastrophe", but said that survivors could still be found.
He said: "We know from previous disasters that some people have remained trapped under buildings for some days."
Anyone wanting to donate to the Red Cross appeal
can call 0207 245 1000.