Sydney  - An Australian leading the aid agency World Vision's relief effort in cyclone-ravaged Myanmar said Monday that interacting with the military regime in South-East Asia's most autocratic country was "incredibly frustrating."

"Clearly, this is politically the most difficult place we have ever worked in responding to a humanitarian crisis," Tim Costello, chief executive of World Vision, told Australia's ABC Radio in a telephone interview from Yangon.

"The government has a very clear message: that it has all the experts and technical capacity needed - it doesn't need any foreigners," he said.

World Vision has 600 local staff in Myanmar and has made it a precondition that they must lead the effort to distribute supplies and not surrender that role to the military.

"The truth is this country doesn't have the capacity," Costello said. "This cyclone's impact is far greater than the [2004 Indian Ocean] tsunami's was in terms of lasting effect on Thailand, Sri Lanka or Indonesia. It's 200,000 square kilometres. It's the rice belt gone."

Costello, a veteran of aid operations around the world, described how difficult it was to help those in the Irrawaddy Delta who are most at risk after a storm that has killed an estimated 100,000 people.

"It's the most unusual humanitarian situation I've ever seen and most of us have ever seen," he said. "You queue for six hours in Yangon just to get petrol, and then there are roadblocks and military clearances to see you have no foreigners or journalists."

Costello said his local staff were returning from the Irrawaddy Delta in tears because there are corpses still unburied and people who have gone for five days without food and water since the May 2-3 cyclone.

"The greatest risk, the nightmare scenario, is waterborne epidemics as the water recedes," Costello said. "Then you get dysentery, malaria, skin infections. If it tips over the edge into cholera and typhoid, then it really is lethal in terms of how it rips through a population already weak and frail."

Costello, an Anglican priest, urged the world not to succumb to frustration and abandon the people of Myanmar.

"It's incredibly frustrating," he said. "When you feel like you want to give up you, have to remind yourself that you have to keep hope alive for those who desperately need it." (dpa)