The United States urged Greeks, Turks and Cypriots to strike a historic deal at unification talks on Wednesday, but Greece described prospects as poor as a midnight deadline approached.
UN Secretary General Kofi Annan was set to announce later on Wednesday a plan to end a 30-year partition even if there is no accord. Absence of agreement however would put the outcome of planned referendums in Greek and Turkish zones in great doubt.
"With today's developments, chances of an agreed settlement seem poor," Greek government spokesman Theodoris Rousopoulos told reporters in the Swiss Alpine resort of Buergenstock where talks are taking place with Turkish parties.
As the clock ticked to Annan's midnight deadline to end talks, there was a frantic rush of diplomacy by both Greeks and Turks, including 11th-hour appeals for help to US Secretary of State Colin Powell by foreign ministers of both countries.
"What I have been saying to all the parties is this is a historic opportunity," Powell told a news conference. "This is the time for leaders to show flexibility, for leaders to be ready to compromise for the greater good of the Cypriot people."
Cyprus is due to join the European Union on May 1, but if the peace plan is rejected in the referendums, only the internationally recognised Greek Cypriot government will join.
This could cement the island's partition and harm Turkey's own hopes of becoming the first Muslim state to join the EU.
The main Cyprus disputes, which have been negotiated for a week, concern how many Greek and Turkish troops will remain on the island, rights to property and freedom of movement between the two sides as well as the rule of EU law.
Disputes over the island have brought Nato partners Greece and Turkey to the brink of war on at least two occasions.