YANGON, Burma — The United Nations warned Friday that it will be forced to ground helicopters that have been ferrying critical aid to Burma's cyclone survivors unless the international community urgently provides more funding.

The UN's World Food Program said it was facing a critical shortage of funds for its logistical operation in the country, including 10 helicopters that have so far delivered lifesaving materials to 60 locations in the devastated Irrawaddy delta.

The use of helicopters, trucks and boats will "grind to a halt by the end of this month unless we get additional funding now," Chris Kaye, WFP's country director in Burma, said in a statement.

The UN estimates that 2.4 million people were affected by Cyclone Nargis and has warned that more than 1 million still need help.

The WFP issued an appeal for $50 million to fund its logistical operation, of which the helicopters are the most expensive to run, but has so far received pledges and funding to cover just 60 percent, the statement said.

Burma's junta faced worldwide criticism after the May 2-3 storm for failing to speed aid to cyclone survivors and initially barring foreign aid workers from the hardest-hit Irrawaddy delta.

Two weeks after the cyclone hit, the reclusive regime authorized the U.N. to use 10 helicopters inside the country.

The helicopters, which were chartered from South Africa, Uganda and elsewhere, provided a crucial boost to aid workers who had been unable to reach hundreds of remote villages in the Irrawaddy delta.

"Of those several hundred villages, we have now reached 60," said WFP spokesperson Paul Risley. "We still have many more villages to reach."

The cyclone killed 78,000 people and left an additional 56,000 missing, according to Myanmar's government.

Separately, EU leaders appealed Friday for the regime to drop its restrictions on international aid agencies seeking to help the victims of the cyclone.

The declaration criticized Burma for holding a referendum on a new constitution just after the cyclone hit.

It also called on Burma's military leaders to release pro-democracy leader Aung San Suu Kyi and other political prisoners.