YANGON (Reuters) - Torrential tropical downpours lashed Myanmar's Irrawaddy delta on Friday, deepening the misery of an estimated 2.5 million destitute survivors of Cyclone Nargis and further hampering the military government's aid efforts.

Despite the latest storm, which is likely to turn already damaged roads to mud in the swamp-covered region, the former Burma's ruling generals insist their relief operations are running smoothly.

However, they issued an edict in state-run newspapers on Friday saying legal action would be taken against anybody found hoarding or selling relief supplies, amid rumours of local military units expropriating trucks of food, blankets and water.

If emergency supplies do not get through in much greater quantities, foreign governments and aid groups say starvation and disease are very real threats.

Some cholera has been confirmed among survivors, but the number was in line with case levels in previous years in Myanmar, the World Health Organization (WHO) said on Friday.

"We don't have an explosion of cholera," Maureen Birmingham, acting WHO representative in Thailand, told reporters in Bangkok.

Diarrhoea, dysentery and skin infections have afflicted some cyclone refugees crammed into monasteries, schools and other temporary shelters after the devastating May 2 storm.

The WHO, which has sent health kits, bleach and chlorine tablets to treat dirty water, said the peak threat from disease was 10 days to one month after a natural disaster.