It said assessments of 55 townships in the Irrawaddy delta and other disaster areas found up to 102,000 people could have been killed in Cyclone Nargis, which struck flimsy dwellings with fierce winds and waves on the night of May 2.

"Based on these assessments, the U.N. estimates that 1,215,885 to 1,919,485 million people have been affected by the cyclone, the number of deaths could range from 63,290 to 101,682, and 220,000 people are reported to be missing," the report by the United Nations Office for Coordination of Humanitarian Affairs said.

Myanmar state-run TV reported on Sunday night that the death toll had risen to more than 28,458 and 33,416 people were missing.

The cyclone had "likely resulted in acute environmental issues that could pose an immediate risk to human life and health", the UN report said.

It said migration and violence were also emerging as problems in the poor southeast Asian country, where a succession of military juntas have ruled with an iron grip for 46 years.

"Given the gravity of the situation including the lack of food and water, some partners have reported fears for security, and violent behaviour in the most severely afflicted areas," the report said.

"Some assessments have suggested that people are coping by migrating outwards from the most affected to less affected areas in search of the basic necessities."

The UN agency also said few visas have been issued for disaster relief workers to enter the country.