YANGON (AFP) - The UN's top disaster official headed Sunday to Myanmar, where the government is under mounting pressure to accept a full-scale relief operation for desperate cyclone survivors in need of immediate aid.

The secretive military rulers have let more foreign experts into the country in recent days to help the estimated two million survivors who do not have enough food, water or shelter more than two weeks after the storm struck.

But with emergency relief coordinator John Holmes due to arrive late Sunday, a UN report said needs were still critical, while British aid group Save the Children said thousands of children could starve to death within weeks.

"We are extremely worried that many children in the affected areas are now suffering from severe acute malnourishment, the most serious level of hunger," said Jasmine Whitbread, chief executive of Save the Children UK.

"When people reach this stage, they can die in a matter of days. Children may already be dying as a result of a lack of food."

Despite thousands of tonnes of aid being flown in, relief groups want fuller access to help supervise relief in the aftermath of the May 2-3 storm, which the government says left nearly 134,000 people dead or missing.

The UN report said that so far about a quarter of the needy survivors had been reached with foreign aid.

The international community has been toughening the rhetoric on the country's military rulers, who are deeply suspicious of the outside world and have limited access to foreigners with expertise in managing disaster zones.

South Africa's Archbishop Desmond Tutu and French Foreign Minister Bernard Kouchner have both raised the spectre of crimes against humanity by the junta over its handling of the catastrophe.

Witnesses who managed to sneak through the security cordon around the hard-hit Irrawaddy Delta said the situation remained dire.

"It was horrible beyond description," said a foreign businessman, one of about a dozen eyewitnesses interviewed by AFP.

"Most of the devastated huts looked like they were empty at first glance. But there were actually survivors inside," he said.

"One hut with no roof was full of about 100 people, crouching in the rain. There was no food and no water. Each person had nothing more than the clothes on their bodies, shivering in the cold."

The junta continues to insist it can handle most of the relief operation by itself and its English-language newspaper, the New Light of Myanmar, on Sunday carried more than two dozen stories praising the regime's relief efforts.

On Saturday, the military authorities ferried a group of foreign diplomats around parts of the pummelled Irrawaddy Delta region, but the top US diplomat in Myanmar said she was not reassured by what she saw.

"The few people that we did see did not resolve my concerns that there's a whole lot of people who received nothing and who have no food, no clean water," Shari Villarosa told AFP.

"I remain hopeful that good sense will strike and they will open up to the international community," she added.

Aid agencies are hoping that the UN's Holmes will have some sway with the generals, who keep an iron grip on one of the poorest and most isolated nations on the planet.

Amanda Pitt, regional spokeswoman for the UN's disaster relief arm headed by Holmes, said he would spend "a few days" in Myanmar.

She said UN Secretary General Ban Ki-moon had "asked him to travel to the region to better assist the survivors and help the government of Myanmar scale up the response to the crisis."

Pitt had no information on which areas Holmes would be able to visit, or if he would have access to the top junta leadership.

Wary of any foreign influence that could weaken its 46 years of iron rule in Myanmar, the military has insisted on managing the relief operation itself and has kept most international disaster experts away.

But aid groups say the government cannot possibly handle the tragedy alone, with hundreds of tonnes of supplies and high-tech equipment piling up in warehouses, bottle-necked by logistics and other problems.

As pressure mounts on Myanmar's allies to use their clout with the regime, Southeast Asian foreign ministers will meet in Singapore on Monday for talks on how to deal with their neighbour.

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