Turkey's prime minister is to join international diplomats at Cyprus peace talks in Geneva, amid signs of progress towards reuniting the divided island.
UN sources said they had not expected Binali Yildirim to come, and it showed how importantly these talks were being viewed, the BBC's James Landale says.
The Geneva talks also involve UK Foreign Secretary Boris Johnson and his Greek and Turkish counterparts.
The Greek- and Turkish-Cypriot communities have been split since 1974.
In that year Turkish troops invaded, following a coup by Greek Cypriots backed by the generals ruling Greece at the time.
Mr Yildirim's presence does not however indicate that a deal is imminent, our correspondent cautions.
For a deal to take effect it would have to win the support of both Cypriot communities in separate referendums.
The UN, overseeing the negotiations, says it is the best chance to reunify the island after four decades of division.
The goal is for the two sides to share power in a two-state federation.
The Greek- and Turkish-Cypriot leaders - Cyprus President Nicos Anastasiades and Mustafa Akinci - on Wednesday exchanged maps proposing territorial boundaries.
It was the first time they had done so, according to the UN, and was hailed as an important advance towards a deal.
New UN Secretary General Antonio Guterres is attending the talks in Geneva, his first foreign trip in the role.
What are the sticking points?
Property: What should happen to the properties that Greek Cypriots had to abandon in 1974? Should they get the right to take their old homes back, or be compensated - and if so by how much?
Security: How can the security of the Turkish Cypriots be guaranteed if Turkey's estimated 30,000 troops leave? Greek Cypriots see them as an occupying force, so should some stay or should Turkey retain the right to intervene?
Who would act as a guarantor of the deal? The EU, of which Cyprus is already a member, or the UK, which has two military bases on the island?
Power and the role of the EU: There is talk of a rotating presidency, but how would that work? And could a Turkish Cypriot president really represent the country from time-to-time at EU summits?
Territory: How much more territory should Greek Cypriots gain to reflect the fact that they make up the majority of the island's population? UN peacekeeping forces estimate that 165,000 Greek Cypriots fled or were expelled from the north, and 45,000 Turkish Cypriots from the south, although the parties to the conflict say the figures are higher.
Turkey still has 30,000 troops stationed in the island's north.
Britain, Turkey and Greece are guarantors of Cyprus's independence, which means they can step in if necessary to restore constitutional order.
Reaching a deal is possible, says Espen Barth Eide, the UN special adviser on Cyprus, though he cautioned that "some of the most complicated and emotional issues" remained outstanding.
While it is unlikely that a "comprehensive settlement" will be agreed in these talks, diplomats and negotiators "will go home with a sense that it is coming", he told reporters.
The maps presented on Wednesday and now locked in a UN vault will form the basis for future discussions on boundaries dividing zones in a federal Cyprus.
