YANGON, Myanmar (AP) – Relief supplies from the United Nations arrived in Myanmar Thursday, but U.S. military planes loaded with aid were still denied access by the country’s isolationist regime five days after a devastating cyclone.

The military junta also continued to stall on visas for U.N. teams seeking entry to ensure the aid is delivered to the victims amid fears that lack of safe food and drinking water could push the death toll above 100,000.

Four airplanes carrying high-energy biscuits, medicine and other supplies arrived in Yangon Thursday, U.N. officials said. Two of four U.N. experts who had flown to Myanmar to assess the damage were turned back at Yangon’s airport for reasons that were not immediately clear, said John Holmes, the U.N. relief coordinator. The other two were allowed to enter.

By rejecting the U.S. offer, the junta is refusing to take advantage of Washington’s enormous ability to deliver aid quickly, which was evident during the 2004 Indian Ocean tsunami that killed 230,000 people in a dozen nations.

“We have demonstrated in crises around the world … our logistical capability to get humanitarian assistance quickly in to the people who need it,” said Shari Villarosa, the top U.S. diplomat in Myanmar.

Gordon Johndroe, President Bush’s national security spokesman, said the U.S. was still working to gain permission to enter Myanmar. Another option being considered was air-dropping aid without permission, said Ky Luu, the director of the U.S. office of foreign disaster assistance.

France has argued that the U.N. has the power to intervene to help civilians because of an agreement by world leaders at a 2005 summit that the international body has a “responsibility to protect” people sometimes when nations fail to do it. But that agreement did not mention natural disasters.

Myanmar’s generals, traditionally paranoid about foreign influence, issued an appeal for international assistance after the storm struck Saturday. They have since dragged their feet on issuing visas to relief workers even as survivors faced hunger, disease and flooding.

In 2004, the first foreign military aid did not arrive in the hardest-hit nation, Indonesia, until two days after the disaster. The most significant help came when U.S. helicopters from the USS Abraham Lincoln began flying relief missions to isolated communities along the coast of Aceh province.

With roads washed out and the infrastructure in shambles, large swaths of Myanmar’s delta region also remain accessible only by air – something few other countries are equipped to handle as well as the United States.

Tim Costello, chief executive of World Vision Australia, said the U.S. has to convince Myanmar’s government that it has no political agenda.

“Clearly we all know the political context there, and I think it’s going to take a little bit more time for a breakthrough there,” Costello said.

Thailand Prime Minister Samak Sundaravej offered to negotiate on Washington’s behalf to persuade Myanmar’s government to accept U.S. aid.

“What is critically needed at this point is for Myanmar authorities to open up to a major international relief effort,” said U.N. spokesman Richard Horesy. “If that is not done quickly, there is a major risk that there will be a second phase to this disaster where large numbers of people will die of communicable disease.”

The Association of Southeast Nations appealed to the international community to keep sending aid through Thailand.

“Please keep the help coming, keep the contributions coming, and if you have to, go to Thailand, park there and wait for redistribution from there,” said ASEAN secretary-general Surin Pitsuwan.

The U.S. military sent more humanitarian supplies and equipment to a staging area in Thailand on Thursday. A C-17 transport plane with water and food landed Thursday, joining the two C-130s in place, Air Force spokeswoman Megan Orton said at the Pentagon. Another C-130 loaded with supplies was on its way, she said.

The Navy also has three ships participating in an exercise in the Gulf of Thailand that could help in any relief effort, including an amphibious assault ship with 23 helicopters aboard.

The Navy was sending helicopters from the USS Essex to the staging area in Thailand, a defense official said Thursday on condition of anonymity because he was not authorized to speak on the record.

The London-based human rights group Amnesty International said some donors were delaying aid for fear it would be siphoned off to the army. The U.N. World Food Program’s regional director, Anthony Banbury, indicated the United Nations had similar concerns.

“We will not just bring our supplies to an airport, dump it and take off,” he said.

So far, the United Nations has recorded donations to Myanmar relief totaling $25 million from 28 nations, the European Union and charities. An additional $25 million has been pledged.

Myanmar’s state media said Cyclone Nargis killed at least 22,997 people and left 42,019 missing, mostly in the hardest-hit Irrawaddy delta. Villarosa said the number of dead could eventually exceed 100,000 because safe food and water were scarce and unsanitary conditions widespread.

“That extraordinary volume of rain, of wave, of wind just crushing everything, snapping everything in its wake, that death toll I think could be conceivable,” said Costello, of World Vision.

U.N. officials estimated as many as 1 million people were left homeless in Myanmar, which also is known as Burma.

In Yangon, the cyclone blew off the roof of Myanmar opposition leader Aung San Suu Kyi and cut the electricity to her dilapidated lakeside bungalow, where she is under house arrest, a neighbor said on condition of anonymity because of the sensitivity of the subject.

Entire villages in the delta were still submerged from the storm, and bloated corpses could be seen stuck in the mangroves. Some survivors stripped clothes off the dead. People wailed as they described the horror of the torrent swept ashore by the cyclone.

“I don’t know what happened to my wife and young children,” said Phan Maung, 55, who held onto a coconut tree until the water level dropped. By then his family was gone.

The World Health Organization has received reports of malaria outbreaks in the worst-affected area, and said fears of waterborne illnesses surfacing due to dirty water and poor sanitation also remained a concern.

Even near Yangon, the country’s largest city, stricken villagers complained that they had received no government assistance and were relying on aid from Buddhist monasteries.

Myanmar’s state television Thursday showed Prime Minister Lt. Gen. Thein Sein distributing food packages to the sick and injured in the delta and soldiers dropping food over villages. The date of the distribution was not given.

Although most Yangon residents were preoccupied with trying to restore their lives, activists wrote fresh graffiti on overpasses, including “X” marks – a symbol for voting “no” in a referendum Saturday on a new military-backed constitution. Voting has been postponed until May 24 in Yangon, some outlying areas and parts of the delta heavily damaged by the storm.

U.N. Secretary-General Ban Ki-moon on Thursday called on Myanmar’s government to postpone the referendum entirely and “focus instead on mobilizing all available resources and capacity for the emergency response efforts.”