A United Nations official has implored Burma's military government to allow foreign aid experts in to help survivors of a vicious cyclone.

"The authorities of the country need to open up to an international relief effort. There aren't enough boats, trucks, helicopters in the country to run the relief effort of the scale we need," said Richard Horsey, a spokesman for UN humanitarian operations in nearby Bangkok, Thailand.

"It's urgent that the authorities do open themselves up."

The British aid group Oxfam said Sunday that in a worst-case scenario, up to 1.5 million people could die from the after-effects of Cyclone Nardis, which struck on May 3.

The official death toll is set at 31,938 with another 30,000 missing, but many Western observers believe the number of dead and missing is much higher, possibly about 100,000.

In a small concession, the first shipment of U.S. aid was allowed to arrive in Burma on Monday.

The humanitarian shipment, which included mosquito nets, blankets and water, was transferred to the Burmese military trucks soon after it arrived in Rangoon.

Two more shipments are to arrive Tuesday.

Two aid groups had planeloads of supplies land in Burma on Monday. Medecins Sans Frontieres sent a plane with 34 tonnes of medical and logistical supplies. Medecins du Monde shipped in 22 tonnes, focusing on emergency first aid kits and medicines to treat malaria and diarrhea.

The Red Cross and World Food Program (WFP) are also flying in relief supplies. The Red Cross hopes to fly in two loads daily.

However, Medicins Sans Frontieres issued a statement protesting "growing restrictions" by the Burmese government on aid movement within the country.

Dana Perino, the White House's presidential press secretary, said the U.S. is prepared to provide an additional US$13 million in food and logistical assistance through the WFP, bringing the U.S. assistance pledge to $16.25 million.

Canada has pledged $2 million in humanitarian aid  so far. There is a Canadian assessment team in Bangkok, Shaun Tinkler, a Foreign Affairs Canada spokesperson, told CTV.ca.

Timely help needed

The aid shipments and commitments to date are seen as a relative trickle relative to the needs.

Burma's military government wants full control of aid distribution, but doesn't have the transportation capability to deliver the volume of assistance needed in a timely manner.

There are roughly 11,000 U.S. Marines in Thailand, with helicopters and other equipment, ready to help in the relief efforts. But the Burmese regime is refusing to allow entry.

Three U.S. Navy ships in the Bay of Bengal could also join the relief effort if given permission, Vice-Admiral Doug Crowder told reporters in Jakarta, Indonesia.

"We need high technology. We need a massive distribution effort in a short time period. Time is running out," Sein Win, Burma's prime minister in exile, told CTV Newsnet.

He thinks aid should be delivered with or without the junta's approval.

In the House of Commons' question period on Monday, government House Leader Peter Van Loan said that Foreign Affairs Minister Maxime Bernier has told the UN Security Council about the need for collective action on getting Burma to allow in outside aid help.

He wouldn't directly address a question by Deputy Liberal Leader Michael Ignatieff on whether the Conservatives supported the "responsibility to protect" principle.

That doctrine states that the international community has a responsibility to protect civilians when their national government fails to do so.

In the Irrawaddy Delta, the worst-hit area, people are surviving in miserable conditions. Many are drinking water from sources contaminated by human feces, corpses or animal carcasses.

"The lives of thousands of cyclone survivors are at extreme risk," aid group World Vision said. "Displaced people are living in appalling conditions in makeshift shelters and camps where overcrowding and unsanitary conditions are prevalent."

Children -- many of them orphans -- are suffering from fever, diarrhea and respiratory infections, it said.

UNICEF Canada, in an email update, said Monday that 2,000 children have been identified as separated from their parents, with the agency working to reunite those families.

UNICEF is working to distribute emergency supplies such as water purification tablets, oral rehydration salts and drums of bleaching powder to purify water supplies.

The organization is also working to set up therapeutic feeding centres in the hardest-hit regions.

With files from The Associated Press