NICOSIA, Cyprus — UN Secretary-General Kofi Annan expressed disappointment Thursday after Cypriot leaders on both sides rejected his reunification plan, dampening hopes for its approval in referendums.

Turkish Cypriot leader Rauf Denktash, meanwhile, urged the United Nations to delay the April 24 vote on the plan, a last-ditch attempt to reunite the island before Cyprus joins the EU on May 1.

The two sides and the Greek and Turkish governments failed on March 29 to reach an agreement of their own after lengthy talks.

Denktash has opposed the plan all along. But UN officials appeared annoyed with Greek Cypriot leader Tassos Papadopoulos, who urged his nation in a televised speech Wednesday night to vote no.

A scheduled meeting between Papadopoulos and UN envoy Alvaro de Soto was abruptly canceled Thursday without explanation.

"I call on the people to vote against approval of the plan in the referendum on April 24 with a strong no," Papadopoulos said. "After judging all the facts ... I am sincerely sorry that I cannot sign acceptance of the Annan plan."

Cyprus has been divided since a 1974 Turkish invasion following an abortive coup by Greek Cypriot supporters of union with Greece. A breakaway Turkish Cypriot state in the north is only recognized by Turkey, which maintains 40,000 troops there.

Papadopoulos said Annan's plan "writes off" the consequences of Turkish occupation of northern Cyprus and legitimizes "the illegal presence of the tens of thousands of Turkish mainland settlers." He said it violates basic human rights and European Union principles ensuring refugees can return to their properties.

Denktash rejects it as failing to protect the rights of Turkish Cypriots, saying it would create "a Greek Cypriot republic."

"Both Papadopoulos and I say 'no' to the plan," Denktash told reporters in Nicosia. "The UN is putting disagreement to a referendum. This is a shame. ... If the UN uses its sense, it would postpone the referendum and continue with negotiations."

However, many Turkish Cypriots favor reunification and see it as a chance for an economic boost. If Cyprus remains divided after May 1, EU laws and benefits will only apply to its internationally recognized Greek Cypriot southern part.

"The secretary-general is disappointed to learn that Mr. Tassos Papadopoulos has now called for rejection of the plan," Annan's spokesman Fred Eckhart said in a statement released in Geneva.

"The secretary-general fully respects the wishes of the people and will not interfere in their decisions. However, he reiterates that Cypriots have a unique opportunity to reunite their country, and he hopes that they will seize it while it is before them," the statement said.

Abdullah Gul, foreign minister of Turkey, which has accepted the plan, said Thursday that Papadopoulos' rejection must be evaluated by everyone "with a cool head and a sense of responsibility."

The Annan plan is a complex document of 200 pages providing a new constitution for the proposed United Cyprus Republic that will replace the existing Republic of Cyprus. The new arrangement will consist of two federal "constituent states," one Greek and one Turkish Cypriot, linked through a weak central government.