Myanmar's refusal to grant visas to foreign aid teams is "unprecedented in modern humanitarian relief efforts", a UN official has said, underscoring mounting frustration over the military governments' response to the cyclone crisis.

Paul Risley, a spokesman for the UN World Food Programme in Bangkok, said the organisation had submitted applications for visas with Myanmar diplomatic missions around the world, but all had been caught up in paperwork.

Some relief supplies have been allowed to land in Myanmar, but many more tonnes of aid and dozens of expert foreign staff have not.

On Thursday the top US diplomat at the United Nations expressed outrage at Myanmar's government for its foot-dragging on allowing in international relief teams in the wake of the Cyclone Nargis disaster.

Zalmay Khalilzad, the US ambassador to the UN, told reporters in New York that the US was "outraged by the slowness of the response of the government of Burma to welcome and accept assistance".

"It's clear that the government's ability to deal with the situation, which is catastrophic, is limited … and since it's not able to you would expect the government to welcome assistance from others," he said.

"We're shocked by the behaviour of the government."

Ban Ki-Moon, the UN secretary-general, has called on the ruling generals to postpone a referendum due on Saturday on the country's constitution.

Only supplies wanted

Myanmar's military government indicated on Friday that while it wanted relief supplies, foreign aid personnel were not being called for.

A foreign ministry statement said the government had given priority to receiving aid from abroad but using its own nationals to deliver it to stricken areas.

The government turned back aid workers and media who arrived on a flight from Qatar carrying emergency supplies on Thursday because they had not been given permission to enter the country, the ministry added.

An estimated one million people have been left homeless and 100,000 may have been killed by the cyclone, according to a US diplomat in the former capital, Yangon, but the government plans to press ahead with the referendum on a new constitution critics say is an attempt by the generals to entrench their rule.

The government allowed in the first major international aid shipment on Thursday but turned away American aid.

Four UN World Food Programme aircraft carrying high-energy biscuits, medicine and other supplies reached Yangon on Thursday, UN officials said.

Relief supplies from Myanmar's neighbours China, India and Bangladesh have also landed.

UN experts turned away

However, two of four UN experts who flew in to assess the damage were turned back at the airport for unknown reasons, said John Holmes, the UN relief co-ordinator.

"I am disappointed that we have not had more results," Holmes told reporters on Thursday.

"We need to continue to urge the government to co-operate," he said.

Many residents remain without food and shelter, while corpses rotting in the flood waters are creating a health hazard.

Describing the situation in Myanmar as "increasingly desperate on the ground", Holmes said Ban Ki-moon, the UN chief, was trying to talk to Than Shwe, Myanmar's military leader, to urge him to "strongly to facilitate access" for foreign relief workers.

"They have opened up to some extent. They have not refused entry [to foreign aid workers]. But they have not facilitated entry... It is not as open as it should be," he said.

But the UN official rejected criticism that he had not been more forceful in pressing Myanmar.

"I do not believe confrontation with the government is likely to result in more help" for the cyclone victims, Holmes said.

Holmes added that the authorities also agreed that customs charges and clearances should be waived for aid delivery, but said it was unclear if the policy had been implemented.

At least 40 visa applications from UN aid workers are pending and many others are waiting in Thailand to enter.

US aid rejected

Among those stranded were 10 members of a USAID disaster response team.

Eric John, the US ambassador to Thailand, told reporters in Bangkok on Thursday that the US was "in a long line of nations who are ready, willing and able to help, but also, of course, in a long line of nations the Burmese don't trust".

"It's more than frustrating. It's a tragedy," he said, adding that each day of delay meant "a lot more people suffering".

A US state department official earlier hinted that it was considering dropping food aid over parts of the disaster zones, without Myanmar's approval.

But the Pentagon said it would not consider such a move without the Myanmar government's permission.

Aside from violating Myanmar's airspace, the US authorities worry that such an unauthorised operation might fail to deliver the airdropped supplies to those most in need.

Robert Gates, the US defence secretary, said the US needed permission from the government but US air force transport aircraft packed with supplies and US navy ships in the area are all ready to enter if permission is granted.

Needed air support

With the Irrawaddy delta's roads washed out and the infrastructure in shambles, large swaths of the region are accessible only by air.

Tim Costello, chief executive of World Vision Australia, said that "it's certainly the case that the Americans, as they showed in the tsunami, have extraordinary capacity".

During the 2004 Indian ocean tsunami, US helicopters from the USS Abraham Lincoln flew missions to isolated communities along the Indonesian coast in the biggest US military operation in South-East Asia since the Vietnam War.

Samak Sundaravej, Thailand's prime minister, has offered to negotiate on Washington's behalf to persuade Myanmar's government to accept US assistance.

France is arguing that the UN has the power to intervene without the Myanmar government's approval to help civilians under a 2005 agreement that the world body has a "responsibility to protect" people when governments fail to do it.

That agreement did not mention natural disasters.

The foreign ministers of France, Britain and Germany have urged Myanmar's leaders to let foreign aid into the country.

In a joint letter in Le Monde newspaper, Bernard Kouchner, the French foreign minister, and David Miliband, the British foreign secretary, urged Myanmar's leaders to "lift all restrictions on the distribution of aid".

Fear of disease

As of early Thursday Myanmar's government has said the confirmed toll stood at 22,980 with more than 42,000 others missing.

With little aid reaching survivors, fears of disease are rising every hour.

Richard Bridle, deputy regional director of Unicef, the UN children's fund, told Al Jazeera that "most people will be drinking bad water and we do have a clear and present danger of that leading on to very contagious diarrhoea diseases".

He said the top priority was to ensure an adequate and safe drinking water supply, but that essential specialist staff were yet to receive visas.

"We badly need to get specialist staff into the country and we would appeal to the authorities in Myanmar to make that entry a lot easier," he said.

PHOTO CAPTION:

A survivor child

Al-Jazeera