A planned US aid flight to Myanmar is not going ahead, the US ambassador to Thailand said on Thursday, saying it was not clear if there had been a mix-up or if the junta had withdrawn permission.

"We don't have permission yet for the C-130 (transport plane) to go in," ambassador Eric John told a press conference.

"I don't know whether they rescinded the decision or if there was a miscommunication," he added.

The US embassy said earlier on Thursday that the junta had agreed to accept US emergency aid after last weekend's devastating cyclone, allowing at least one American plane to deliver supplies.

John told reporters that the United States was still hopeful US aid workers would be allowed in, despite signs to the contrary from the Myanmar, formally known as Burma, which has been stalling issuing visas to many aid workers.

"I'm optimistic that the Burmese leadership is going to make the right decision on visas, make the right decision on C-130 or other assistance," he said. Cyclone Nargis pounded the country's low-lying south late on Friday-Saturday, killing nearly 23 000 people by the regime's official count.

The United States has urged Myanmar's military rulers to accept international disaster relief after the top US diplomat in Yangon warned that more than 100 000 people may have died.

"It should be a simple matter. It's not a matter of politics. It's a matter of a humanitarian crisis," US Secretary of State Condoleezza Rice said on Wednesday.

An official from the US government aid arm USAID said that some US supplies have already been sent to Myanmar through the United Nations.

AFP