"We're outraged by the slowness of the response of the government of Burma (Myanmar) to welcome and accept assistance," U.S. Ambassador to the U.N., Zalmay Khalilzad, told reporters.

"It's clear that the government's ability to deal with the situation, which is catastrophic, is limited."

The U.N. food agency and Red Cross/Red Crescent said they had finally started flying in emergency relief supplies after foot-dragging by Myanmar's ruling military junta. The United States was waiting for approval to start military flights.

U.N. Secretary-General Ban Ki-moon said he was seeking direct talks with the junta's senior general, Than Shwe, to persuade him to remove obstacles. A U.N. spokeswoman said Ban believed it might be "prudent" for the government to postpone a constitutional referendum planned for May 10.

U.S. ambassador Eric John told a news conference in Bangkok earlier that the United States and Thailand thought the Myanmar generals had agreed to let a U.S military cargo plane fly in supplies to the reclusive southeast Asian country.

But that turned out to be premature.

"We don't have permission yet for the C-130 to go in, but I emphasize 'yet'" John said.

Approval for such a flight would be significant, given the huge distrust and acrimony between the former Burma's generals and Washington, which has imposed tough sanctions to try to end 46 years of unbroken military rule.

Witnesses have seen little evidence of a relief effort under way in the Irrawaddy delta region that was swamped in Saturday's storm. It was the worst cyclone in Asia since 1991, when 143,000 people were killed in neighbouring Bangladesh.

"We'll starve to death if nothing is sent to us," said Zaw Win, a 32-year-old fisherman who waded through floating corpses to find a boat for the two-hour journey to Bogalay, a town where the government said 10,000 people were killed.

The storm pulverized the delta on Saturday with 190 km (120 mph) winds followed by a massive 12-foot (3.7-metre) wave that caused most of the casualties and damage, virtually destroying some villages.

The United Nations estimated at least 1.5 million people in Myanmar have been "severely affected," U.N. humanitarian affairs chief John Holmes said.

Holmes told reporters he was "disappointed" with the lack of progress being made in getting U.N. aid in.