YANGON - The 1.5 million people left destitute by Myanmar's devastating cyclone were increasingly desperate on Wednesday, as foreign aid remained at a trickle and overstretched aid workers struggled to reach hard-hit areas.

In a token and late concession to critics who say outside aid is critical, Myanmar's reclusive military rulers invited 160 personnel from neighbouring Bangladesh, China, India and Thailand to assist in delayed and sometimes chaotic relief efforts.

But it is a fraction of the thousands of foreign aid workers needed for a "tsunami-style" international aid operation from the May 3 cyclone, which left up to 100,000 people dead or missing in the Irrawaddy delta.

"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 by phone from Yangon.

Thailand's prime minister flew to Myanmar's main city of Yangon to try to persuade Prime Minister Thein Sein to let more foreign experts into areas pulverised by the early May storm.

Samak Sundaravej is hoping for more luck than United Nations and Western officials, whose similar efforts have had little success.

Some have suggested food and other urgent supplies may have been diverted by Myanmar's ruling junta rather than going straight to helpless victims, many homeless and some barefoot.

However, a World Food Programme (WFP) spokesman in Bangkok said of high-energy food it had sent: "We collected the biscuits at the (Yangon) airport and they remain in our possession."

In any case, experts said the relief effort - further complicated by heavy rains and the threat of a possible second cyclone - is only delivering a tenth of the supplies needed.

A tropical depression was swirling southwest of Yangon on Wednesday and a U.S. advisory warned it could develop into a cyclone in the next 24 hours.

"It's terrible. This is always another worry when you have a major disaster, that you have further hazards affecting people," Amanda Pitt, spokeswoman for the U.N.'s humanitarian affairs office, told a news conference in Bangkok.

GREATER TRAGEDY

The international community has flown in tonnes of medicine, food and shelter materials, but getting it to low-lying delta area has been complicated by poor equipment, bad weather and government intransigence.

Heavy rains have pelted the low-lying delta region, slowing the transportation of aid by land and adding to the misery of tens of thousands of refugees sandwiched into monasteries, schools and pagodas.

The international community has warned of an even greater tragedy if the aid effort is not ratcheted up.

Lacking food, water and sanitation, survivors of Cyclone Nargis face the threat of killer diseases such as cholera and in some areas are waiting in vain for help to arrive.

"If these people aren't reached and aid got to them quickly, and shelter and toilet facilities, disease will break out," the International Rescue Committee's Bacon said.

The WFP said it was looking for helicopters to airlift rice and high-energy biscuits down to the delta and also boats to reach isolated communities along the Irrawaddy river.

It said it had provided food to 50,000 people and aimed to reach 750,000 over the next six months.

Operations in Myanmar are a shadow of the massive international relief operation kick-started just days after the 2004 Asian tsunami.

The United States alone deployed thousands of its military and more than a dozen ships in the Indian Ocean, and many other countries provided major help.

But Myanmar's junta has made it clear it does not want Westerners distributing aid.

Foreign experts in sanitation, nutrition and medicine have either been prevented from entering the country formerly known as Burma or are restricted to Yangon.

Armed police send back foreigners who attempt to pass through checkpoints surrounding the former capital.

In a statement after emergency talks on Myanmar in Brussels on Tuesday, EU development ministers called on Yangon "to offer free and unfettered access to international humanitarian experts, including the expeditious delivery of visa and travel permits."

The EU ministers stopped short of endorsing a French call to deliver supplies if necessary without the junta's permission.