UN secretary general Antonio Guterres has said talks opening on Monday in Geneva between Greek and Turkish Cypriot leaders will provide a "historic opportunity" to reunite the island after 42 years of division.
Cypriot president Nicos Anastasiades and Turkish Cypriot leader Mustafa Akinci seek to narrow differences on key issues before Wednesday, when Mr Guterres is to chair a conference bringing together the Cypriots with Greece, Turkey, Britain, the European Union and UN Security Council members.
Britain assumed the role of guarantors of the Cypriot republic at independence in 1960.
The objective is agreement on a framework for a two-canton Cypriot federation, which would reunite the island split in 1974 when Turkey occupied the north following a failed coup by the Greek junta.
Mr Anastasiades and Mr Akinci have negotiated since May 2015. During recent months, their teams worked continually while the two men met several times a week under the auspices of UN envoy Espen Barth Eide, a former Norwegian foreign minister.
Mr Eide has said that “if it was only up to the Cypriots this problem would be solved”. In spite of the involvement of outside nations, he said that “the possibilities [of a settlement] are higher than ever”. The UN will continue its efforts if a deal is not achieved at Geneva.
The sides continue to disagree over the size of the Turkish Cypriot canton. The Greek Cypriots argue it must be reduced from the current 36.5 per cent of the island to 28.2 per cent while the Turkish Cypriots insist on 29.2 per cent. Areas to be added to the Greek Cypriot canton are disputed.
Mr Akinci calls for a rotating presidency and continuation of a Turkish military presence in the north and Turkish security guarantees with the right of intervention. Greek Cypriots hesitate to accept an alternating presidency and reject deployment of Turkish troops and any guarantee.
Heavy pressure
Although EU foreign policy chief Federica Mogherini said the bloc could provide guarantees for both communities, Mr Anastasiades recently suggested a Turkish guarantee could be accepted for a limited time.
While Greece has kept its distance, the negotiators have been under heavy pressure from Turkish president Recep Tayyip Erdogan, who has threatened to annex northern Cyprus if there is no deal acceptable to Ankara.
Turkey maintains 35,000 troops in the north, where at least 150,000-160,000 mainland Turkish citizens have settled permanently, and it subsidises the breakaway Turkish state, which is recognised only by Ankara.
The internationally recognised Greek Cypriot majority republic is a member of the EU, which regards the north as an area outside the control of the government.
Mr Eide estimated it could take three months to fill in the details of an agreement and three months to explain it to Greek and Turkish Cypriots before separate referendums in mid-2017.
In April 2004, Turkish Cypriots voted for a UN-crafted plan for a federation but Greek Cypriots rejected it, arguing it favoured the Turkish side. Since these negotiations have been between the two leaders, Mr Eide has said, “Every letter, word and sentence will have been written by Cypriots.”
Such a deal would be a first. Even independence was negotiated by Britain, the colonial power, Greece and Turkey.