Hopes for a peace deal in Cyprus stalled Friday over a decades-old dispute, with the rival sides at loggerheads over the future of Turkish troops on the divided island.

A week of UN-brokered talks in Geneva between Greek Cypriot President Nicos Anastasiades and Turkish Cypriot leader Mustafa Akinci sparked optimism that an agreement to reunify the island could be at hand.

But any settlement will require an agreement on Cyprus's future security, with consent needed from key players Greece, Turkey and former colonial power Britain -- who all joined the talks Thursday.

The eastern Mediterranean island has been divided since 1974, when Turkish troops invaded in response to an Athens-inspired coup seeking union with Greece.

And a key sticking point remains the presence of some 30,000 Turkish troops in the north of the island.

Ankara and Akinci have insisted that some Turkish military presence is essential for Turkish Cypriots to feel safe in a prospective united country.

Anastasiades on Friday restated his position that a timeline must be agreed for those troops to eventually withdraw.

And Greek Foreign Minister Nikos Kotzias said there can be no solution to the four-decade division of Cyprus while Turkish "occupation" troops remain.

"A just solution (to division) means, first of all, eliminating what caused it, namely the occupation and presence of occupation forces," Kotzias said, according to a ministry statement as he left Geneva.

But Turkish President Recep Tayyip Erdogan declared that a full withdrawal of Turkish troops from northern Cyprus was "out of the question".

He said in televised remarks that Athens and Greek Cypriots still have "different expectations" from their Turkish and Turkish Cypriot counterparts on resolving the Cyprus problem.

Cyprus is often described as one of the most militarised places on earth with the presence of UN peacekeepers, Turkish troops, two sovereign British bases and a Greek army contingent.

- 'A grave mistake' -

Asked about Erdogan's remarks, UN envoy Espen Barth Eide insisted that efforts to end one of the world's longest running political crises would not be derailed over a temporary war of words.

Discussions on security had just begun and the issue is "highly emotional", he said.

A 1960 agreement gave Britain, Greece and Turkey the right to intervene to defend Cyprus's sovereign integrity, which Ankara used to justify its invasion.

Eide said that by joining the peace process, the camps had accepted that this so-called "guarantor power" system was destined to change.

Britain and Greece have said they were happy to scrap the deal, but for Turkey it remains a priority.

Akinci struck a more moderate tone on the issue than Erdogan.

Letting the talks fail would be "a grave mistake", he said, calling the guarantor power deal "a system (that) belongs to 1960."

"Now we are in 2017," he added. "How do we adapt this system through a mutually accepted formula which will secure the security concerns of Turkish Cypriots but at the same time would not cause any threat for the other community?"

Technical experts from all sides were due to reconvene in Switzerland on January 18 to table concrete proposals for a new security pact.

- 'Cannot create winners and losers' -

The UN process is aimed at forging a republic with two zones that would be a full European Union member.

Despite the roadblocks ahead, Anastasiades said the two sides were "on a path that creates hope" and that compromise was key.

"A solution cannot create winners and leave losers (in its wake). If we want it to be viable and durable, all must understand, Greek and Turkish Cypriots alike, that a fine balance must be struck," he told reporters in Geneva.

Earlier in the week, the rival sides tackled thorny domestic questions like the composition of a unified government and land swaps.

In an unprecedented moment, they exchanged maps late Wednesday detailing their visions of how internal boundaries should be redrawn.

Turkish Cypriot leaders have accepted to return some of the land they have controlled since the failed 1974 coup, although disputes remain over certain areas and a final version has not been agreed.

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