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ATLANTA, May 8 (Reuters) - U.N. Secretary-General Ban Ki-moon said on Thursday he had requested talks with senior Myanmar general Than Shwe over a humanitarian crisis in the country but nothing had been scheduled.

The United Nations believes that at least 1.5 million people in Myanmar have been "severely affected" by Cyclone Nargis.

"I am trying to reach and talk directly to senior general Than Shwe of Myanmar to urge him to allow aid workers to deliver this urgent food aid with a sense of great urgency," Ban said during a visit to Atlanta. "I have requested telephone talks with him ... nothing has been scheduled yet."

Ban urged the government of Myanmar to open its borders to aid and said U.N. relief workers should be exempted from all visa requirements.

In a separate statement issued by his office at the U.N. headquarters in New York, Ban suggested that it might be "prudent" for Myanmar's government to postpone a referendum on a military-drafted constitution because of the cyclone that has devastated the country.

Ban said he "has taken note of the government's decision to proceed with the constitutional referendum on 10 May, while postponing it in some of the areas most affected by the cyclone."

"Due to the scope of the disaster facing Myanmar today, however, the secretary general believes that it may be prudent to focus instead on mobilizing all available resources and capacity for the emergency response efforts," the statement said.

(Reporting by Matthew Bigg and Claudia Parsons; Editing by Sandra Maler)

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