Talks aimed at ending the decades-long dispute in Cyprus entered a crucial stage on Monday, as U.N. Secretary-General Kofi Annan unveiled a revised reunification plan for the Mediterranean island.

Mr. Annan gave the document to senior Turkish Cypriot, Greek Cypriot, Turkish and Greek officials who are meeting in the Swiss resort of Buergenstock in a final bid to resolve differences.

All sides in the talks have given the U.N. secretary-general a mandate to finalize the reunification plan himself, if no agreement is reached by March 31.

The accord then will be submitted in separate referendums to both Cypriot communities on April 20. If either side rejects the plan, only the Greek part of the island, which has an internationally recognized government, will enter the European Union on May first and enjoy membership benefits.

There is no information yet on what is in the revised reunification plan. An earlier deal called for Greek Cypriot and Turkish Cypriot states, held together by a loose federal government.

The Turkish Cypriots are demanding limits to the number of Greek Cypriots who would be allowed to return to their old homes in what is now Turkish Cypriot territory. Turkish Cypriots also want the same political recognition Greek Cypriots enjoy.

The reunification talks moved to Switzerland from Nicosia after a month of meetings between Greek Cypriot and Turkish Cypriot leaders failed to resolve differences between the two sides.