YANGON (Reuters) - The first U.S. military aid flight to Myanmar landed in Yangon on Monday but emergency supplies remained at a trickle for 1.5 million people facing hunger and disease in the cyclone-ravaged Irrawaddy delta.

The C-130 military transport plane flew in from an air base in neighboring Thailand carrying water, mosquito nets and blankets as U.S. President George W. Bush condemned Myanmar’s military leaders for being either “isolated or callous.”

The junta’s navy Commander-in-Chief Soe Thein received the U.S. supplies, which were accompanied by Admiral Timothy Keating, head of the U.S. Pacific Command, and Henrietta Fore, administrator of the U.S. Agency for International Development.

A stream of other aid flights had already landed in Yangon, but only a fraction of the help needed has got to people in the flooded delta, partly because the junta has kept foreign aid and logistics experts out of the country or in Yangon.

In New York, U.N. Secretary-General Ban Ki-moon made clear his exasperation with the junta and its “unacceptably slow” response to Cyclone Nargis since it struck Myanmar on May 3.

Bush, who shortly before the cyclone had imposed fresh sanctions on Myanmar to pressure it toward democratic rule, said in a radio interview with CBS that the junta was apparently more interested in power than in its people.

Noting the leaders had moved the capital away from the biggest city Yangon, he said: “either they are isolated or callous.”

Fore told reporters in Bangkok she had won permission to fly in two more planes on Tuesday but there was no breakthrough on letting foreign helicopters and boats ferry supplies into the delta.

“It’s a good first step,” she said, adding U.S. aid was increasing to $16 million, from $3.5 million.

Delivery of the U.S. aid shipment was broadcast on the tightly controlled Myanmar state television.

Keating said the U.S. navy would have three ships in international waters off the coast of Myanmar in 36 to 48 hours. It also had 4,000 Marines and a “large number” of cargo-carrying helicopters on stand-by in Thailand.

“We’re limited only by the permission from the authorities in Burma,” he said at the Thai air base.

WAITING FOR VISAS

“We think we need to be moving 375 tonnes of food a day down into the affected areas. We are doing less than 20 percent of that,” World Food Program spokesman Marcus Prior said in the Thai capital Bangkok.

At the United Nations in New York, Ban delivered his most critical comments so far of the Myanmar authorities’ response and said: “We are at a critical point.”

“Today is the 11th day since ... Nargis hit Myanmar,” he told reporters. “I want to register my deep concern -- and immense frustration -- at the unacceptably slow response to this grave humanitarian crisis.

Myanmar’s reclusive military government was accepting aid from the outside world, including the United Nations, but refused to admit foreign experts waiting in Bangkok for visas from the Myanmar Embassy.

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The United Nations said its top representative in Myanmar had flown to Naypyidaw, the generals’ new capital, on Monday to hand over a list of 60 critical U.N. and relief agency staff.

U.N. humanitarian affairs chief John Holmes told reporters in New York the United Nations had disbursed $20.3 million from its emergency relief fund to cover costs related to urgent needs, such as food, shelter, sanitation and health.

He said there were still problems with visas though the situation had improved somewhat. “It was confirmed that 34 visas for United Nations relief staff from the different agencies will now be granted or are being granted,” he said.

But U.N. officials said none of its staff in Bangkok had received visas on Monday. They said foreign staff inside the country were prevented from leaving Yangon.

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In its latest assessment of the scale of the disaster, the U.N. humanitarian agency said between 1.2 million and 1.9 million people were struggling to survive and the number of dead could range from 60,000 to 102,000.

Myanmar state television raised its official toll to 31,938 dead and 29,770 missing on Monday. Most of the casualties were killed by the 12-foot (3.5 meter) wall of water that hit the delta, with the cyclone’s 190 kph (120 mph) winds.

RAIN FORECAST

People throughout the delta were crammed into monasteries, schools and other buildings. Displaced people flooded into towns that were barely able to cope with the influx.

Lacking food, water and sanitation, they faced diseases such as cholera. Heavy rain was forecast for the delta this week, which could further hinder the relief effort.

People from Yangon were loading food and water into their vehicles and taking it to villages outside the city in the absence of any organized aid effort.

The cyclone raged through an area that is home to nearly half of the country’s 53 million people and about 5,000 sq km (1,930 sq miles) of land remained under water. The cyclone ravaged some of the country’s main rice-growing areas.

The United Nations has launched an appeal for $187 million to support the survivors for at least three months. The WFP is seeking $56 million to buy food for 630,000 people for six months.

France was sending a warship carrying 1,500 metric tons of rice which was expected near Myanmar later this week. Paris says it wants to distribute the food directly itself, but will not do so without authorization.

British Prime Minister Gordon Brown said on Monday Britain was sending a navy ship to the region to help humanitarian operations.