(Adds opposition reaction)

YANGON, May 15 (Reuters) - Myanmar's army-drafted constitution was overwhelmingly approved in the first phase of a two-stage referendum after a devastating cyclone, state radio said on Thursday.

More than 92 percent of the ballots cast in last Saturday's first-round vote were in favour of the charter, a key step in the military government's seven-stage roadmap to democracy, which critics say will only entrench army rule.

Voting in areas hardest hit by Cyclone Nargis, which has killed up to 128,000 people and left another 2.5 million destitute, will be held on May 24, the junta has said.

The process is meant to culminate in multi-party elections in 2010 and bring to an end nearly five decades of military rule in the Southeast Asian country.

The new charter gives the military an automatic 25 percent of seats in parliament, control of key ministries and the right to suspend the constitution at will.

The referendum, the first national vote since the 1990 election, which the generals lost by a landslide to Aung San Suu Kyi's National League for Democracy, has been widely derided by Western governments and the opposition.

"This referendum was full of cheating and fraud across the country," NLD spokesman Nyan Win said.

In some villages, authorities and polling station officials ticked the ballots themselves and did not let the voters do anything," he added.

The government had vowed to go ahead with the vote in parts of the country not affected by Cyclone Nargis, but postponed it by two weeks in the devastated Irrawaddy delta and the storm-ravaged former capital of Yangon.

While the military has appealed for outside help for disaster victims, it has been reluctant to allow a full-scale international relief effort, delaying the approval of visas and landing rights for aircraft carrying urgently needed supplies.

(Reporting by Aung Hla Tun; Writing by Darren Schuettler; Editing by Jerry Norton) (For stories on Myanmar cyclone click on [nSP152717 or follow link to Reuters AlertNet http://www.alertnet.org)

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