The main priority is to provide for those made homeless

The United Nations team in Bam said the search might be called off on Sunday, although a final decision would be taken by the Iranians.

Meanwhile Interior Minister Abdolvahed Mousavi Lari said the total number of dead was likely to exceed 20,000.

Up to 15,000 bodies had already been "recovered and buried", he said.

About 400 foreign experts have joined rescue efforts in Bam.

Iran has appealed for medicine and equipment to help the tens of thousands hurt in the south-eastern city.

Thousands of survivors spent a second night sleeping in the open or in their cars, fearful of aftershocks.

Work then resumed on the grisly task of digging through the ruins of some of the many collapsed buildings.

I faced a very, very sad story: all of the buildings were destroyed and most of the streets were full of sand and dust Mustafa, Bam Tell us your experiences Pictures of the earthquake

The BBC's Jim Muir, in Bam, says most of the destroyed structures were made of mudbrick or ordinary bricks which collapsed leaving no protected spaces where people might survive.

John Holland, of rescue team Rapid UK, described the scene from the air: "We're probably looking at about 80% of the buildings totally flattened.

"Time is against you, the weather is against you, the type of buildings are against you. Obviously there is a small window of opportunity."

US pledge

Work has barely begun on the ruins of Bam's historic citadel, a 2,000-year-old architectural marvel with a big medieval city clustered around it.

Whole buildings simply crumbled to the ground

The whole enormous site has been reduced to a sea of dust and rubble and no-one knows how many people may lie buried here.

Pope John Paul prayed for the people of Bam on Sunday and urged the international community to help the Iranian victims.

"May the solidarity of the entire world, felt particularly in the atmosphere of Christmas, make their situation less dramatic," he said in his Sunday address in St Peter's Square in Rome.

A long list of nations have sent or pledged aid to Iran - including the United States, which branded Iran part of the "axis of evil" along with Iraq and North Korea.

Two US planes carrying food and other aid landed in Kerman, the provincial capital, early on Sunday - the first US aircraft to land in Iran for a decade.

Huge task

The authorities' main priority is to provide food, water and shelter to those made homeless.

But the scale of this disaster is such that a monumental challenge of rehabilitation and reconstruction lies ahead, our correspondent says.

Bam and the surrounding area is home to more than 200,000 people.

The earthquake quake had a magnitude of at least 6.3, according to Iranian sources, while the US Geological Survey measured it at 6.7.