BBC NEWS | Asia-Pacific | 'No access' to Burma cyclone zone
Aid agencies say supplies are urgently needed in affected areas
Burma's junta has tightened access to areas hit by Cyclone Nargis, despite pleas to allow in foreign aid workers.
A UN official says the regime has erected more checkpoints to ensure foreigners cannot reach affected areas.
The latest official figures put the death toll at almost 38,500 with 27,838 more missing, state radio said.
The UN says up to 2.5m people need urgent aid and has called a meeting of regional and donor nations to discuss "all options" on aid.
UN Secretary-General Ban Ki-moon said Wednesday's meeting of donors and the Association of South-East Asian Nations would discuss the "mobilisation of resources and aid workers".
He "regretted" the UN had spent much of its time arranging rather than delivering help.
"Even though the [Burmese] government has shown some sense of flexibility, at this time it's far, far too short," he said.
Meanwhile, forecasters say another cyclone is forming off Burma's coast.
The Hawaii-based Joint Typhoon Warning Center said on its website that "a significant tropical cyclone" could develop in the next 24 hours.
Dire warnings
Aid agencies are warning that the ruling generals' refusal to sanction a major international relief effort will cause more deaths.
Chris Kaye, the Burma director for the UN's World Food Programme, said the generals were trying to ensure no foreigners were allowed into the affected areas by beefing up security on checkpoints.
"There is absolutely no progress in getting foreign experts out into the field," he said.
Undercover reporter says aid is still in short supply in Burma
Aid agencies fear the death toll could be far higher than official estimates.
The Red Cross said it had studied figures from 22 organisations and warned the toll could be as high as 128,000.
UN humanitarian affairs chief John Holmes said the organisation had revised up its estimate of 1.5m people "severely affected" by the cyclone to between 1.6m and 2.5m.
Thai leader Samak Sundaravej held talks with the junta, but failed to broker a deal on access for foreigners.
Mr Samak flew to Rangoon for talks with Burmese Prime Minister Thein Sein, aimed at persuading the junta to allow more foreign aid workers access.
But he said Gen Thein was adamant the military needed no outside help.
"He insisted that his country with 60 million people has a government, its people and the private sector to tackle the problem by themselves," Mr Samak told reporters in Bangkok after his day trip to Burma.
EU envoy Louis Michel is heading for Burma for a three-day visit, where he says he will urge the generals "to be more open-minded and more understanding".
But he told the AFP news agency that his chances of success were "slight".
The continuing diplomatic efforts come amid more dire warnings of the consequences of the cyclone.
The UN's food agency says Burma will face food shortages if farmers cannot return to their fields in the next 90 days.
The UN's food agency fears Burma will face food shortages
"If we are not able to plant before the monsoon, we will have a serious shortage of rice in the country," said Leon Gouws, of the Food and Agriculture Organisation.
Another UN body, the International Organisation for Migration, says it may already be too late to save the many victims who are in need of aid.
"Maybe we should already be looking at rebuilding projects instead of emergency relief," said the IOM's Chris Lom.
"There's been an opportunity lost - in terms of immediate response, maybe we're too late for that."
Residents have told the BBC's Burmese service how private citizens have been trying to distribute water and supplies from their own cars - but soldiers have been confiscating the goods.
A BBC correspondent in Burma described aid delivery as "unco-ordinated and piecemeal".
He said one devastated village - with one-quarter of its 400 houses left standing - had received just one bag of rice from the government.