(U.N. humanitarian affairs office corrects number of dead and missing from its situation report on the Myanmar cyclone. A U.N. official said its estimate of 220,000 missing was incorrect. The official also corrected the number of assessed townships to 38 from 55)

BANGKOK, May 11 (Reuters) - Up to 100,000 people may be dead or missing in the Myanmar cyclone, the United Nations humanitarian agency said on Sunday, warning of environmental damage, violence and mass migration.

Following assessments of 38 affected townships, it estimated that between 60,000 and 100,000 people were dead or missing in Cyclone Nargis, which struck flimsy dwellings with fierce winds and waves on the night of May 2.

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

The reclusive military government, while accepting aid from all over the world, has been reluctant to allow in western aid experts, many of whom have been waiting in Bangkok and other cities for days. (Reporting by Darren Schuettler; Editing by Grant McCool)

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