YANGON, Myanmar - The United Nations has received permission from Myanmar to use nine helicopters to ferry relief supplies to stranded cyclone victims, U.N. Secretary-General Ban Ki-moon said yesterday, as he warned that relief efforts were at a "critical moment."

"We have received government permission to operate nine WFP [World Food Program] helicopters, which will allow us to reach areas that have so far been largely inaccessible," Ban told reporters in New York before departing for Myanmar.

His announcement was not immediately confirmed by officials of Myanmar's military government.

"I believe further similar moves will follow, including expediting the visas of [foreign] relief workers seeking to enter the country," Ban said. "I'm confident that emergency relief efforts can be scaled up quickly."

The announcement came as Myanmar's leaders began three days of mourning for the dead and missing. Flags at government offices, schools and large hotels flew at half-staff, but shops opened and many people in Yangon said they had little idea what the official mourning entailed.

U.N. Undersecretary-General for Humanitarian Affairs John Holmes was in Myanmar seeking to persuade the junta to let in more international assistance and paving the way for Ban's visit.

The junta appears to be slowly relenting to foreign pressure to accept more outside help, but even foreign aid workers already in the country are still banned from the most devastated areas. The United Nations said only a fraction of survivors had gotten any international assistance.

The official death toll stood at about 78,000, with 56,000 more people missing. Conditions in the low-lying Irrawaddy River delta remained precarious, with survivors facing disease, malnutrition, and exposure to the elements.

Speaking at a news conference a day after visiting the delta, Holmes said he had suggested the junta make "better use of international expertise and assets" and ensure "all possible routes in for aid are open, whether they be by land or sea or air."

The U.S. military has several helicopters on standby on a warship off the Myanmar coast and in neighboring Thailand.

The United States is already flying supplies in from Thailand on C-130 cargo aircraft at a rate of about five flights a day. But the planes go to Myanmar's biggest city, Yangon, from which it is a difficult journey to the Irrawaddy Delta.

Ban is expected to visit areas devastated by Cyclone Nargis as well as talk with officials and aid workers. On Sunday, he is scheduled to attend a meeting of aid donors in Yangon. Myanmar, one of the world's poorest nations, claims losses from the disaster exceeded $10 billion.

At U.N. headquarters, Ban was optimistic that aid efforts could be increased and welcomed the junta's "recent flexibility" in allowing relief workers from the 10-member Association of Southeast Asian Nations to begin distributing aid.

State-owned media quoted Senior Gen. Than Shwe, the junta leader, as saying the government has spent $45.5 million on relief operations, has met immediate needs such as food, shelter and health care, and is moving into the reconstruction phase.

Foreign aid agencies and U.N. officials were less upbeat.

"I think there is still a long way to go to improve the relief efforts, to speed it up and to make sure that all the people who are in need are reached," Holmes said. "There is still a major effort to be mounted on the relief side, which has to go on for some three to six months."

"Everything in the path of the tidal surge has been almost completely destroyed, including villages," he said.