Talks to reunify war-divided Cyprus have failed, U.N. Secretary General Kofi Annan announced Tuesday as he left all-night negotiations with Greek and Turkish leaders on the Mediterranean island.

"We have reached the end of the road," Annan said, signaling the end of months of intense efforts to reunite the island split into Greek and Turkish sides since 1974.

Annan had used Cyprus' impending entry into the European Union to pressure Greek Cypriot President Tassos Papadopoulos and Turkish Cypriot leader Rauf Denktash to agree on a federation plan that would bring the two sides together under a single weak central government.

The talks stumbled over Turkish insistence that their breakaway Cypriot state win full recognition, and demands by the Greeks for the right of refugees to return to homes in northern Cyprus that they left 29 years ago.

"The efforts to salvage the project of a united Cyprus ... regretfully have not proved successful," Annan said.

Annan huddled with special envoys from Greece, Turkey and Britain for several hours after Papadopoulos stormed out of the talks accusing Denktash of rejecting Annan's reunification proposals. The U.N. chief failed to come up with a package that would rescue the plan.

"The Annan plan is not acceptable," Denktash said, complaining that the proposal to allow a limited return of Greek refugees would require 100,000 Turkish Cypriots to leave their homes -- a figure contested by the Greek community.

Annan brought the two leaders to The Hague on Monday to get their commitment to submit his reunification plan to their communities in a referendum.

Greek officials said their side agreed in principle to hold a popular vote, but Denktash told reporters, "this was not a plan we could ask the people to vote on."

Details of the final negotiations were not known, but Annan had been expected to offer amendments to his plan and an extension of the March 30 deadline for the approval by the two Cypriot communities in separate referendums.

Annan left open the possibility of resuming the talks at a later stage. "My plan remains on the table" for the two leaders to pick up whenever they are ready, he said.

At the same time, he said he was instructing his special envoy to Cyprus, Alvaro de Soto, to close his office on the island and return to New York to prepare a full report.

Annan said he shared "a deep sense of sadness" with residents of the island. "I am not sure another opportunity like this one will present itself again any time soon."

If the plan had been approved by the Greek and Turkish communities, Cyprus could sign an accession agreement with the European Union on April 16 as a united country.

Without agreement, the whole of Cyprus will be accepted as a member, but with provisions for EU laws to apply to the breakaway Turkish north only after the island is reunited.

Despairing at the leaders' inability to reach agreement after decades of talks, Annan came up with the referendum idea after Turkish Cypriots staged mass demonstrations in favor of the plan and certain Greek Cypriot politicians and newspaper columnists expressed support.

Cyprus has been split since Turkey invaded in 1974 in the wake of an abortive coup by supporters of union with Greece. The breakaway state in the north, about one-third of the island, is only recognized by Turkey, which maintains 40,000 troops there.