The UN has told international donors that the long-term rebuilding of the Iranian quake-hit city of Bam could cost up to $1 billion (£543 million).
Bam's residents will need aid for years to come
The estimates, released in a UN report, were given to representatives from nearly 50 countries in Geneva.
The UN and the Red Cross had earlier appealed for $73m to help the quake victims over the next three months.
Some 30,000 people died in the earthquake, and about 100,000 Bam residents have been left homeless.
On Thursday, media attention refocused on Bam after a man was pulled alive from rubble, 13 days after the earthquake struck.
There is little, if any, chance of finding more survivors, but aid organisations do not want people to forget Bam, says the BBC's Imogen Foulkes.
"At present, initial estimates indicate that the long-term recovery could cost anywhere between $700m to $1bn," the UN's Flash Appeal report said.
"Although most of these resources will have to be garnered by the Government... of Iran, the international community can provide critical support in... the implementation of this large-scale multi-year programme," it said.
"It will therefore be important to utilise the next three months to identify these areas of co-operation, plan for the medium and long-term recovery and reconstruction."
Elizabeth Byrs, spokeswoman for the UN Office for the Co-ordination of Humanitarian Affairs (OCHA), told BBC News Online the reconstruction would last "at least two years".
"That's a minimum estimate," Ms Byrs added.
At Friday's meeting, the UN was also giving the donors a detailed rundown on its needs in Bam over the next three month after it appealed for the additional $73m.
Meanwhile, the World Health Organisation (WHO) has said in the long term $30m will be needed to restore the city's health service.
Half of all Bam's health workers were killed in the tremor.
A priority now is mental health, says the WHO, as many survivors are bereaved and traumatised.
The WHO alone has appealed for $4m for immediate medical relief.
"The health needs now are ones of normalising the systems, of finding all the family members, of helping them through a very difficult period, and then getting on with the business of reconstruction," said Dr David Hayman, a specialist in communicable diseases with the WHO.
Suffering 'just started'
The UN said it had raised $74m in aid for victims of the quake but said more money was needed.
"I have never met people having lost as many family members and as many relatives as the people of Bam. Some 30,000 people died in the course of a few hours," Jan Egeland, UN humanitarian co-ordinator told the BBC.
"A priority is shelter. People cannot continue to live in tents. We must get the water and sanitation systems working and we must provide people with an income," he said.
"The suffering of the Bam people has just started."
More than 40 countries sent aid to Iran soon after the quake.