With up to 100,000 people feared killed in Burma's cyclone and an estimated 1 million homeless, frustration grew on Thursday over the military government's inability to allow international aid into the country.

Six days after Cyclone Nargis pulverised the Irrawaddy Delta with 190 kmh (190 MPH) winds followed by a tidal wave, aid was barely trickling into one of the world's most isolated and impoverished countries.

Three planes loaded with vital U.N. emergency supplies for Burma's cyclone victims were delayed on Thursday, awaiting clearance from the military government hours after they were due to land, U.N. officials said.

"They need assistance today. They needed it yesterday," Tony Banbury, Asia regional director of the U.N. World Food Programme WFP, said in Bangkok.

"They can't wait and they shouldn't be asked to wait until tomorrow and it's crucial that food, water, shelter and medical supplies need to go in right away."

Another WFP official said the three planes were waiting on tarmacs in Bangkok, Dhaka and Dubai with 38 tonnes of supplies.

The WFP officials said they believed one Thai commercial cargo plane had landed in Yangon with seven tonnes of high-energy biscuits.

CLUTCHING TREES

Cyclone Nargis, which means "daffodil" in Urdu, slammed into coastal towns and villages in the rice-growing delta southwest of Yangon on Saturday, the most devastating storm to hit Asia since 1991, when 143,000 people were killed in neighbouring Bangladesh.

WFP spokesman Paul Risley said aid agencies normally expect to fly in experts and supplies within 48 hours of a disaster, but nearly a week after the Burma cyclone, few international relief groups have been able to send reinforcements into Burma.

Witnesses reported that villages were destroyed and people fought for survival by clutching trees as the storm brought walls of water charging inland from the sea.

Aid has been trickling in from other Asian nations, but governments and relief agencies are putting increasing pressure on Burma's reclusive military rulers to throw their borders wide open to as much help as possible.

Reports of cyclone damage in a country that used to be the world's largest rice exporter added to worries about tight global supplies of the grain.

The U.N. Office of the Coordination of Humanitarian Affairs said 5,000 square km (1,930 square miles) of the delta were under water.

The government insists it has enough rice reserves, although the U.N.'s Food and Agriculture Organisation said damage to crops and storage buildings in the delta could mean that Burma will need short-term imports and miss its 2008 export targets.

At the United Nations in New York, John Holmes, U.N. undersecretary-general for humanitarian affairs, said four Asian aid workers who did not need visas would get in but other U.N. aid workers were still waiting for travel permits.

The United States and other Western countries have imposed tough sanctions against Burma over its human rights record, punitive measures that have antagonised the government.

The Burma military has its own aid and resettlement operation. State news broadcasts showed soldiers loading emergency supplies onto helicopters before dropping it off in the devastated delta area. They also showed senior military figures visiting survivors in hospitals and handing out food and water.

But land convoys to the inundated Irrawaddy delta were nowhere to be seen, a Reuters witness said.

State media are reporting a death toll of 22,980 with 42,119 missing, although diplomats and disaster experts said the real figure from the massive storm surge that swept into the Irrawaddy delta is likely to be much higher.

"The information that we're receiving indicates that there may well be over 100,000 deaths in the delta area," Shari Villarosa, charge d'affaires of the U.S. embassy in Burma, said in a teleconference with reporters in Washington.

Political analysts and critics of 46 years of military rule said the cyclone may have long-term implications for the junta, which is even more feared and resented since last September's bloody crackdown on Buddhist monk-led protests.