The C-130 transport plane carried more than 12 tonnes of emergency supplies, including desperately needed equipment to provide clean drinking water to victims of the cyclone that hit 10 days ago, officials said.

The United States has offered a far broader relief effort in Myanmar, including navy ships and helicopters that could deploy in the hardest-hit regions of the Irrawaddy Delta, but so far the junta has declined.

"All of us are optimistic that this C-130 will be the first of many. The world has much to offer," US ambassador to Thailand Eric John told reporters shortly before the plane took off. "We offer our assistance without condition."

But convincing the military that US aid comes with no strings attached won't be easy, analysts said.

The junta regularly attacks the United States in state media, accusing Washington of aiding Aung San Suu Kyi's opposition party and of training dissidents.

The regime's suspicions have been hardened by US sanctions imposed a decade ago over rights abuses and Aung San Suu Kyi's detention.

Since the Iraq war, junta leader Than Shwe has also become nervous that Washington could be planning some kind of regime change in Myanmar, analysts said.

"Burmese generals, especially General Than Shwe, are very paranoid," said Win Min, a Myanmar military analyst based in Thailand.

"With a military plane, they will worry that the US military is doing spying from the sky. They will be really worried about that," he said. "By allowing them to fly, it is a significant concession."

The United States is prepared to send two more flights on Tuesday, but still has not received final approval from the junta, said a spokesman for the US embassy in Bangkok.

While small US planes do regularly fly to Yangon with supplies for the embassy there, experts said Monday's flight marked the most significant US aid to the country in more than two decades.

"The last time there was any kind of major US assistance to the country would have been in the 1970s and the 1980s, when the US gave counter-narcotics assistance," said Dave Mathieson, a researcher with Human Rights Watch.

The anti-drugs programme was suspended after the military crushed a major pro-democracy uprising in 1988, when the US suspended most aid to the country.

During the uprising, the US evacuation of its embassy staff aroused the suspicion of the generals, who were spooked by the movement of a naval ship close to Myanmar's territorial waters, Win Min said.

"It was purely for the evacuation of the US staff. But still some generals don't believe in it," he said. "They have their suspicions."

Fear that the United States could mount an invasion by sea was one reason Than Shwe moved the capital from the port city of Yangon to a remote bunker in the centre of the country.

If this first aid flight goes well, Win Min said, it could open the door to at least some future cooperation for cyclone victims.

"I hope the Burmese generals will cooperate with the US," he said. "Look at the tsunami. The US did the best, sending the helicopters" to help victims in Indonesia.

"None of our regional powers have that capacity."

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