UN humanitarian affairs chief John Holmes told reporters that there were now between 1.6-2.5 million people who were "severely affected" by Cyclone Nargis and urgently needed aid, up from a previous estimate of at least 1.5 million people.

Thai Prime Minister Samak Sundaravej said after a two-hour meeting in Yangon, where he urged his counterpart Thein Sein to ease visa rules for relief workers, that he was told Myanmar could "tackle the problem by themselves."

In New York, UN Secretary-General Ban Ki-moon, who has expressed frustration over the response by Myanmar's reclusive leaders, met key donor states and Asian powers to discuss "what kind of concrete measures we can do from now on."

"Even though the Myanmarese government has shown some sense of flexibility, at this time it is far, far too short," he said. "The magnitude of this situation requires much more mobilization of resources and aid workers."

Among those invited were the United States, Britain, France, Russia, China, India, Bangladesh, Australia and Japan.

TRICKLE OF AID

Nearly two weeks after the cyclone swept through the heavily populated Irrawaddy delta rice bowl, killing tens of thousands of people, foreign aid still amounts to little more than a trickle.

Myanmar, formerly called Burma, was once the world's biggest rice exporting country but more than 40 years of military rule have left it impoverished. The military junta has repeatedly crushed pro-democracy movements and tightly restricts visits by foreigners.

Samak told reporters in Bangkok that Myanmar's leaders had insisted that teams of foreign experts, who have been refused entry, were not needed.

"They are confident of dealing with the problem by themselves. There are no outbreaks of diseases, no starvation, no famine. They don't need experts, but are willing to get aid supplies from every country," Samak said.

Louis Michel, the top European Union aid official, disagreed. "There is a risk of water pollution. There is a risk of starvation because the storages of rice have been destroyed," he told reporters in Bangkok.

"We want to convince the authorities of our good faith. We are there for humanitarian reasons," he said. He threw cold water on suggestions from some European countries that foreign countries move unilaterally to bring in aid.

Adm. Timothy Keating, the commander of US forces in the Pacific, also rejected that idea. "We have absolutely no intention of forcefully providing relief supplies," he said in an interview with National Public Radio.

He said US flights of emergency aid would continue for the time being, even though Myanmar was refusing permission for US officials to monitor, or help with, distribution.

A senior US military official in Washington said there were signs that aid was stacking up at Yangon airport and said Washington was keen to get permission to fly helicopters to the worst-affected areas.

The official said there were reports that some 230 camps had been set up to house more than 230,000 displaced people. "They're springing up all over the place," he said. "The problem they have is a lack of water and sanitary facilities."

Officials said despite reports that some supplies were being stolen or diverted by the army, the humanitarian needs were so great that they would keep making deliveries -- while continuing to urge that US aid workers be granted visas.

ACCESS IS "CRITICAL"

World Food Program chief Josette Sheeran said in Washington her organization had so far reached 28,000 people.

"A critical issue now is access," she said. "Our flights are allowed to bring in some supplies, but far from enough - a massive effort is needed to save lives..." she told a US Senate hearing on the global food crisis.

Holmes was asked if the United Nations might have to consider air drops to get food and other aid to cyclone victims who have not been helped and who are crowded into Buddhist monasteries and schools.

He said it was not an ideal form of distributing aid but added, "It is something that could be contemplated" if barriers to aid workers were not lifted.

He also warned that epidemics of diseases like cholera, malaria and measles "can break out at anytime now."

One group of Christian doctors has been treating children in churches, operating below the government's radar. "We have to try to do something," said one Asian doctor from the group, giving out medicine to children for diarrhoea in a rickety wooden church in a village just north of Yangon.

More heavy rain and winds were forecast in the delta as a tropical depression moved in, but the UN weather agency discounted fears that a new cyclone was forming.

Myanmar state television raised its official toll to 38,491 dead, 1,403 injured and 27,838 missing on Wednesday.

The International Federation of the Red Cross estimated on the basis of reports from 22 organizations working in Myanmar that between 68,833 and 127,990 people had died.

In a gesture to critics, Myanmar's rulers invited 160 personnel from Bangladesh, China, India and Thailand to assist in the sometimes chaotic relief efforts but that was a fraction of the number needed, experts said.

"It's just awful. People are in just desperate need, begging as vehicles go past," Gordon Bacon, an emergency coordinator for the International Rescue Committee, told Reuters from Yangon.

(Additional reporting by Darren Schuettler, Nopporn Wong-Anan, Carmel Crimmins amd Pracha Hariraksapitak in Bangkok; Louis Charbonneau at the United Nations; Susan Cornwell and Missy Ryan in Washington)