Cyprus is one of the world's longest-running political crises and the UN-backed talks that began in the Swiss alpine resort of Crans-Montana on June 28th had been billed as the best chance to end the island's 40-year division.
The failure to reach a deal brings an end to more than two years of UN-backed efforts to resolve the conflict.
"I am deeply sorry to inform you that despite the very strong commitment and engagement of all the delegations and the different parties ... the Conference on Cyprus was closed without an agreement being reached," UN secretary-general Antonio Guterres told reporters.
Cyprus has been divided since 1974 when Turkish troops invaded and later occupied its northern third in response to an Athens-inspired putsch seeking union with Greece.
Guterres himself was upbeat when he first joined the Crans-Montana talks late last week, describing the negotiations as "highly constructive", and urging the rival Cypriot sides to seize "a historic opportunity to reach a comprehensive settlement to the conflict that has divided Cyprus for too many decades".
But the tone quickly soured and the UN chief flew back to Switzerland early Thursday in a bid to try to end the stalemate that had set in.
He held a full day of back-to-back meetings with President Nicos Anastasiades, the Greek-Cypriot leader, and his Turkish-Cypriot counterpart Mustafa Akinci, as well as the foreign and European affairs ministers from so-called guarantor powers Greece, Turkey and Britain.
EU foreign policy chief Federica Mogherini was also there to show support for the process.
And US vice president Mike Pence called Anastasiades and Akinci urging them to "seize this historic opportunity to reunify the island ... to the benefit of all Cypriots," according to the White House.
But after pushing negotiations into Friday, just hours before he was set to leave for the G20 summit in Hamburg, a drawn-looking Guterres was forced to acknowledge that the talks ended "without a result."
Shortly before his announcement, a source close to the negotiations told AFP the talks had become heated: "There was people yelling, a lot of emotions."
Guterres himself said "it was obvious that there was still a significant distance between the delegations on a certain number of issues, and a deal was not possible," he said, without providing more details.
But during the past week, it became clear the negotiations had run into trouble over security guarantees and the withdrawal of Turkish troops, among other things.
Greek foreign minister Nikos Kotzias earlier in the week called for the withdrawal of Turkey's "occupying troops", while Ankara retorted that "Turkey will not step back on the issue of security and guarantees."
Turkey maintains more than 35,000 troops there, and any prospects of reunification largely hinge on a drastic reduction of Ankara's military presence.
Several previous peace drives have stumbled over the issue, with Greek Cypriots demanding a total withdrawal of what they say is an occupying force and minority Turkish-speakers fearful of ethnic violence in the event of a pullout.
Despite the lack of an agreement, Guterres on Friday hailed the efforts of the two Cypriot leaders and their communities to find common ground.
And with UN mediator Espen Barth Eide by his side, he praised the UN team that had "done everything possible to bring closer the positions."
Guterres stressed that while the Crans-Montana conference had proved fruitless, "that doesn't mean that other initiatives cannot be developed in order to address the Cyprus problem."
"The United Nations role is the role of a facilitator and we will be always at the disposal of the parties willing to come to an agreement if that would be the case," he said.