Bangladesh has appealed for more international aid to deal with a national crisis after the “unimaginable” destruction caused by the worst cyclone to hit the country in a decade.

Fakhruddin Ahmed, the head of the military-backed emergency Government, said that about four million people had been affected by Cyclone Sidr last week, and the death toll – currently nearly 3,500 – was rising.

“We are faced with a national crisis. I hope that the people will come forward to help those affected,” he said in a televised address. “The destruction of houses, roads, trees and crops by the hurricane is unimaginable.”

The Category 4 cyclone swept across the Bay of Bengal and crashed into the southern coast of Bangladesh on Thursday evening, with 155mph winds causing a 6m (20ft) tidal wave in some coastal areas.

It was the worst natural disaster in Bangladesh, which has a population of 150 million, since 1991 when a cyclone and storm surge killed about 143,000 people.

While officials put the death toll at between 3,400 and 3,500 yesterday, the Bangladesh Red Crescent Society says that the final figure could be as high as 10,000.

The United Nations estimates that more than 273,000 homes have been destroyed and 650,000 damaged in the country – one of the poorest and most densely populated in the world.

International aid worth about $142 million (£69 million) has so far been pledged, with the UN granting $8.75 million yesterday and the European Commission announcing an aid package of $9.6 million.

Britain said yesterday that it would provide £2.5 million for immediate relief efforts and would “consider further funding over the next few months”.

But most of the money has yet to arrive and aid workers say that washed-out roads, fallen trees and a shortage of boats have prevented them from getting tents, rice and drinking water to many survivors.

Officials in the affected areas - inhabited by fishermen and farmers – also say that lack of drinking water and medicine has caused outbreaks of diarrhoea.

“People here are resilient. However, the scale is such that it will take months for people to be able to return to their normal lives,” said Heather Blackwell, the Bangladesh head of Oxfam.

“It could take weeks before we know exactly how bad this cyclone was.” The disaster is now testing the limits of the emergency Government, which took power in January after months of political violence led to a state of emergency and the cancellation of elections.

The Government has promised to clean up the country’s notoriously corrupt and violent politics before organising new elections by December next year, but has been criticised for excessive use of force. Mr Ahmed said that about 3,000 soldiers, two cargo planes, twelve helicopters and ten ships were working to distribute aid.

Two American C130 transport aircraft and two US naval vessels are expected to join them, according to Henrietta Fore, the director of US Foreign Assistance and USAid.

“President Bush has asked me to inform you that both civilian and military assistance would come in the next days for the cyclone victims,” she told reporters on a visit to Dhaka, the Bangladeshi capital. Washington has already pledged $2.1 million in emergency aid.

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