Iranian officials say they now believe at least 41,000 people were killed in last month's devastating earthquake.
Tens of thousands of survivors were left homeless
The previous official death toll in the ancient city of Bam had been 30,000.
The final number could still be revised, perhaps reaching 45,000, said Mohamed Mohamadi Kalbaykani, a senior aide to Iran's supreme leader.
His statement, quoted by the official Irna news agency, came during a second visit by Ayatollah Ali Khamenei to the region hit by the 26 December tremor.
"This is a great catastrophe," Mr Kalbaykani was quoted as saying of the quake which destroyed about 70% of the city's buildings.
Workers are still sifting through the rubble and recovering more bodies.
Consideration is also being given to the tens of thousands left homeless by the disaster, Mr Kalbaykani said.
"All officials have to give their full attention to Bam. Their efforts so far deserve recognition, and these efforts should be accelerated," he added at a ceremony in the city.
"The leader says Bam must be rebuilt, so his orders must materialise."
International agencies such as the United Nations and Red Cross have been raising money and sending supplies to Bam, where the long-term cost of reconstruction is estimated to be $1bn.