By Michele Kambas and Tulay Karadeniz
GENEVA (Reuters) - Talks to resolve the decades-old division of Cyprus ended without agreement on Thursday but with a plan for officials to reconvene on Jan. 18 to tackle its thorny security question, before a fresh attempt to forge a political deal.
The east Mediterranean island has been partitioned between ethnic Turks and Greeks since 1974, when Turkish forces invaded in response to an abortive Athens-inspired coup aimed at union with Greece. An accord has eluded generations of diplomats and NATO allies Greece and Turkey have come at times to the brink of war over Cyprus, a former British colony.
U.N. Secretary-General Antonio Guterres told Reuters he was confident that the participants in talks were determined to make a "last effort" to find a solution.
There was no precise date set for the guarantors of the process - the Greek, Turkish and British foreign ministers - to meet again, but officials said they would reconvene once the sides had codified their positions.
"The discussions today underscored the participants’ intention to find mutually acceptable solutions on security and guarantees that address the concerns of both communities," a U.N. statement said.
"They recognized that the security of one community cannot come at the expense of the security of the other. They also acknowledged the need to address the traditional security concerns of the two communities while at the same time developing a security vision for a future united federal Cyprus."
Guterres had earlier said there could be no "quick fix" in the rift.
The parties are trying to reach a security deal on the presence of Turkish forces on the island in tandem with political negotiations on a comprehensive federal settlement sought by islanders.
Greek Cypriots want the guarantor system dismantled because of Turkey's 1974 invasion. Turkish Cypriots, targeted by Greek Cypriot nationalists before the war and after the breakdown of a post-independence power-sharing arrangement, want it maintained.
"Our position, and the Turkish Cypriot side's position on this matter is the same. The guarantorship of Turkey and the existence of Turkish soldiers on the island will continue," Turkish Foreign Minister Mevlut Cavusoglu told reporters.
"This is an indispensable demand of the Turkish Cypriot people and the most sensitive issue for them."
It was Guterres's first major involvement in a conflict which has been on the world body's agenda for more than half a century and hosts one of its longest-serving peacekeeping forces.
In a 2004 referendum, a U.N. reunification blueprint was approved by Turkish Cypriots but rejected by Greek Cypriots, who represent Cyprus in the European Union.
Recent hydrocarbon discoveries off Cyprus's shores could help the EU reduce its energy dependence on Russia.
Diplomats believe Nicos Anastasiades and Mustafa Akinci, respective leaders of the island's Greek and Turkish Cypriots, represent the best chance in years to reunite the island.
But there are obstacles ranging from property grievances of thousands uprooted in conflict to more practical difficulties associated with power-sharing and security.
"The fact that we have got this far is a real tribute to the courage and the determination of the leaders of the Greek Cypriot community and Turkish Cypriot community," British Foreign Secretary Boris Johnson said in a Facebook post.
In a groundbreaking move on Wednesday, the sides submitted proposals on how to define the post-settlement boundaries. Under the proposals, Turkish Cypriots would retain between 28.2 and 29.2 percent of total Cypriot territory, down from about 36 percent now.
Britain has offered as part of any final peace deal to relinquish about half of the 98 square miles it still administers - equivalent to 3 percent of total Cypriot territory.
(Additional reporting by Alastair Macdonald in Malta, Marina Depetris, Tom Miles and Stephanie Nebehay in Geneva; Writing by Michele Kambas; Editing by Tom Miles and Andrew Hay)