NICOSIA (Reuters) - Rival Cypriot leaders meet in the Swiss Alps this week in a make or break summit to find a peace deal ending decades of division for the partitioned island. The omens are not good.

A barricade made of barrels is seen at the UN-controlled buffer zone in Nicosia, Cyprus June 26, 2017.REUTERS/Yiannis Kourtoglou

The United Nations has called estranged Greek and Turkish Cypriot sides to open-ended talks in the Alpine resort of Crans-Montana on June 28.

Their goal is a peace deal uniting Cyprus under a federal umbrella and which could also define the future of Europe’s relations with Turkey, a key player in the conflict.

Two issues stand out; Turkish Cypriot demands for a rotating presidency, and Greek Cypriot demands that Turkey pull all its troops off the island, and renounce its intervention rights.

Publicly, neither side is willing to budge. Greek Cypriots, in a further complication, have issued an advisory to drill for natural gas in mid-July, plans vehemently opposed by Turkey which says the island nation has no jurisdiction.

“My expectations are rather low,” said Hubert Faustmann, Professor of History and Politics at the University of Nicosia.

Divided in a Turkish invasion in 1974 triggered by an abortive coup by seekers of union with Greece, mediators say the two sides have come closer than they ever had to a deal, but the hard chapters have been left until last.

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Diplomats hope leaders Nicos Anastasiades and Mustafa Akinci can strike a deal with the backing of Greece, Britain and Turkey. Those three countries are guarantor powers of Cyprus under a treaty which granted the former colony independence in 1960.

Greece and the Greek Cypriots want the guarantor system dismantled. The system allows any of the three countries to intervene to restore constitutional order.

Turkey and Turkish Cypriots want the guarantor system, or some vestige of it, to remain in place. But if there is a compromise on that, everything else should fall into place.

“It will all depend on the security chapter ... If they agree it will be a success, a breakthrough. If it doesn’t it will be a failure,” Faustmann said.

On the eve of the summit, both sides have stood their ground. A Turkish Cypriot official engaged in talks told Reuters that sharing a rotating presidency was a ‘sine qua non’, or non-negotiable, for their side.

Christoforos Fokaides, the Greek Cypriot defense minister, reiterated the position of his side on Sunday.

Any deal, he said, must allow peaceful co-existence on the island “without occupation troops, and the anachronism of guarantees”. Turkey has some 30,000 troops in northern Cyprus, a breakaway Turkish Cypriot state. Greeks want them gone.

Stars have been on alignment over Cyprus before, only to be blown spectacularly apart.

Any deal must pass separate simultaneous referenda in both communities. A previous endeavor by the UN in 2004 flopped when Greek Cypriots rejected the reunification blueprint.

“There have been 50 years of negotiations. We have to make up our minds,” said the Turkish Cypriot official involved in negotiations.

“Are we going to tell people we have a good deal? It might not be perfect but if you want to reach perfection you can talk a few more decades.”