Burmese children line up to receive free rice after the destructive Cyclone Nargis on the outskirts of Rangoon on Monday. (Associated Press)

United Nations Secretary General Ban Ki-moon harshly criticized Burma's military regime Monday, describing its response to the devastating cyclone that hit the country 10 days ago as "unacceptably slow."

Speaking at the United Nations in New York, Ban Ki-moon said he was "immensely frustrated" at the pace of aid delivery and relief to some 1.5 million victims of Cyclone Nargis.

Ban also said that despite repeated attempts to contact Burma's senior general, Than Shwe, he had been unable to speak with him and had sent him a letter Monday.

The UN and other international aid officials have been calling for days for the reclusive military junta in Burma, also known as Myanmar, to relax its restrictions on foreign aid workers coming into the country and allow more relief flights to land.

Burma has granted relatively few visas to foreign aid workers, and only a handful of flights carrying emergency supplies from foreign donors and agencies have been allowed into the country. The first U.S. military flight arrived Monday after more than a week of negotiations between Washington and the Burmese regime.

Even so, the mosquito nets, water purification technology and emergency rations that it carried are being distributed by Burmese soldiers, not aid workers.

American officials say they will be watching closely to make sure the U.S. aid isn't siphoned off by Burma's government as some have alleged has occurred in other cases.

Two more American air shipments are expected to get clearance to fly in on Tuesday.

Another four U.S. military ships and 11,000 military personnel stationed in southeast Asia are ready to help with the aid mission, but it is unclear whether the military junta that rules Burma has any intention of giving the troops and equipment clearance to enter its borders.

Members of Myanmar Fire Department and army soldiers help unload relief supplies from a U.S. cargo plane parked at the international airport in Rangoon on Monday. (Associated Press)

Also Monday, two planes carrying aid from humanitarian groups based in Europe were allowed to land in the country. Flights from the Red Cross and the UN's World Food Program have also been delivering relief supplies, but United Nations officials said the aid was a small fraction of what was needed.

Richard Horsey, a spokesman for UN humanitarian operations in Bangkok, said clean drinking water, shelter, medical support and food were sorely lacking.

"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," he said.

The government, which wants full control of relief operations, has fewer than 40 helicopters, most of them small or old. It also has only about 15 transport planes, primarily small jets unable to carry hundreds of tonnes of supplies.

Strained relations keep aid gates closed

Burma has strained relations with the international community, including the U.S. government, which has imposed economic and trade sanctions on the country in response to the policies of the military junta.

Villagers work in a town devastated by the May 3 cyclone in Twantay township, in southern Burma, on Friday. (Associated Press)

Burma, in response, has blocked certain countries from delivering aid in the aftermath of Saturday's cyclone, and is holding up approval for most visas sought by foreign workers who wish to reach the survivors.

One of the few international agencies to get relatively free access to the storm-hit areas is the Red Cross. Speaking to CBC news from Rangoon, Red Cross official Joe Lowry said the most immediate needs were medicine and clean water.

"Ten days after a disaster like this," Lowry said, "we have a lot of standing water and we can expect a spike in diarrheas and mosquito-borne diseases. It's a serious situation."

He said the Red Cross hoped to be able to provide a million litres of fresh water a day in the worst affected areas, using purification tablets and filters.

Burmese state media said Monday that 31,938 people had died since the cyclone hit, while international aid organizations say the death toll could be more than 100,000. Tens of thousands of people are reported missing, while many more have been forced to flee their homes.

Burmese criticize regime

In the Irrawaddy River delta, thousands of people have converged on local Buddhist monasteries, where they are sleeping in cramped conditions. Drinking water in the area has become contaminated by feces and the dead bodies of people and animals.

Heavy rains are forecast for the week, and the annual monsoon season is set to begin in several days. Aid officials warn this will make living conditions even worse in remote areas of the delta that are already waterlogged by the tidal surge from the typhoon.

"So far we have enough water by collecting rain, but we do not have food anymore," said U Patanyale, an abbot of a monastery in the delta town of Pyapon, who also had some harsh words for his country's regime.

"The government is very controlling," said Patanyale.

"Those who want to give directly to the victims get into trouble. They have to give to the government or do it secretly. They follow international aid trucks everywhere. They don't want others to take credit."

While the country copes with the devastation, counting is underway following a referendum held Saturday on a new constitution intended to maintain the military's grip on power. Many in the international community, including the UN, had urged Burma to postpone the election and focus on helping cyclone survivors.

The referendum proposed constitutional changes that include guaranteeing 25 per cent of parliamentary seats to the military and allowing the president to hand over all power to the military in a state of emergency.

With files from the Associated Press