YANGON, Myanmar () - A U.S. plane ferried relief to Myanmar for the first time Monday to help nearly 2 million cyclone victims facing disease and starvation, but both President Bush and the U.N. chief strongly criticized the military junta over its response to the deepening crisis.

Even as the death toll climbed, Myanmar's authoritarian regime continued to bar nearly all foreigners experienced in managing humanitarian crises from reaching survivors of Cyclone Nargis.

With hundreds of thousands of homes destroyed in the disaster zone, refugees packed into Buddhist monasteries or camped in the open, drinking dirty water contaminated by dead bodies and animal carcasses. Medicine and food were sorely lacking - even as supplies bottled up at the main international airport.

Yangon, Myanmar's largest city, was pounded by heavy rain Monday and more downpours were expected throughout the week, further hindering aid deliveries. For many, the rainwater was the only source of clean drinking water.

U.N. Secretary-General Ban Ki-moon chided the junta for its "unacceptably slow response" in helping victims of the disaster.

"Unless more aid gets into the country - very quickly - we face an outbreak of infectious diseases that could dwarf today's crisis," he said. "I therefore call, in the most strenuous terms, on the government of Myanmar to put its people's lives first."

President Bush told CBS News that the world should be angry and condemn the military government.

"Here they are with a major catastrophe on their hands, and (they) do not allow there to be the full kind of might of a compassionate world to help them," Bush said.

Myanmar's hermetic authoritarian regime made a huge concession Monday by letting the United States - the fiercest critic of its human rights record - bring in relief following prolonged negotiations.

It appeared to broaden the original agreement for three flights on Monday and Tuesday, with a U.S. Marines spokesman saying the flights would continue Wednesday.

The U.S. military C-130 cargo plane filled with 14 tons of water, mosquito nets and blankets was unloaded in Yangon, providing what officials said was help for some 30,000 victims of the May 3 disaster.

It was immediately transferred to Myanmar army trucks to be ferried by air force helicopters to the worst-hit Irrawaddy delta, government spokesman Ye Htut told reporters.

A U.S. second flight carrying over 19,000 pounds of relief took off Tuesday.

The United Nations said its first aid convoy arrived Monday evening in Yangon overland from Thailand with more than 20 tons of tents and plastic sheets. Distribution of the U.N. aid began Tuesday.

Lt. Col. Douglas Powell, the U.S. Marines spokesman for the operation, said the U.S. will do whatever it can to ease the suffering. "It's really just up to what the Burmese will allow us to do."

The U.S. ambassador to Thailand, Eric John, was more direct.

"It is important that we, and the international community, be allowed to help," he said. "Let them in. Let them save lives."

The official death toll from the cyclone rose by nearly 3,500 Monday to 31,938, with another 30,000 missing; the United Nations and others have said the death toll could reach 100,000 or higher.

The first British aid flight packed with plastic sheets to provide shelter to more than 9,000 families was also on its way to Yangon.

"The lives of thousands of cyclone survivors are at extreme risk," the World Vision aid group 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. Many survivors complained of getting rotting rice while soldiers kept the best food for themselves.

Two planes carrying 56 tons of medical and other aid from Europe-based humanitarian groups also arrived in Yangon on Monday. Three more planes were en route, said Medecins Sans Frontieres, decrying the "growing restrictions" by the military on the movement of aid within the country.

Myanmar's government has less than 40 helicopters, most old and in disrepair, and some 15 transport planes, primarily small jets unable to carry hundreds of tons of supplies.

"The authorities of the country need to open up to an international relief effort," said Richard Horsey, a spokesman for U.N. humanitarian operations, in Bangkok, Thailand.

"There aren't enough boats, trucks, helicopters in the country to run the relief effort of the scale we need. It's urgent that the authorities open themselves up."

Adm. Timothy J. Keating, the commander of the U.S. military in the Pacific, was on board Monday's relief flight to try to negotiate with the junta for a larger U.S. role.

Some 11,000 U.S. service members and four ships are in the region for an annual military exercise and could be used to help the aid mission, U.S. Marine spokesman Lt. Col. Douglas Powell said.

In addition, three U.S. Navy ships in the Bay of Bengal were sailing closer to Myanmar, ready to aid cyclone victims if they are given permission, Vice Adm. Doug Crowder told reporters in Jakarta, Indonesia.

Calls mounted, meanwhile, for airdropping aid into the country, with or without the junta's approval.

"The sands of time are running out," said Britain's opposition Conservative Party leader David Cameron, suggesting aid should be airdropped into Myanmar if the junta does not provide access soon.

"In the end, what matters is getting aid through to people and feeding them and stopping them from dying," he told BBC Radio.

Some experts said that was unlikely.

"Well, I don't think anybody now at this stage is seriously considering airdropping," said Terje Skavdal, head of the U.N. Office for the Coordination of Humanitarian Affairs. "I think the issue now is trying to build the best possible relationship with the government to get the best possible access."

U.S. Defense Secretary Robert Gates said last week he could not imagine dropping aid without the consent of authorities and British Prime Minister Gordon Brown seemed to agree.

However, French Foreign Minister Bernard Kouchner said airdrops could be allowed under the U.N.'s "responsibility to protect" mandate, and discussions were under way on a possible U.N. resolution requiring Myanmar's government to open its doors to more aid.

Andrew Kirkwood of Save the Children, who heads the international agency's Myanmar operation, lauded Myanmar's private sector for "picking up a lot of the slack" by selling aid groups clothing, materials for shelter and other relief supplies at cost price.