In a statement on Friday UN Security Council warned that any move to resettle the former tourist town would be "inadmissable".
The UN Security Council has demanded "the immediate reversal" of a unilateral decision by Turkey and Turkish Cypriot leaders to reopen the island's abandoned suburb of Varosha.
Once a tourism hub, Varosha has lain empty and mostly fenced-off since the 1974 invasion that split Cyprus.
On Tuesday, Turkish Cypriot leader Ersin Tatar announced that a 3.5 square kilometre section of the ghost town would revert from military to civilian control.
Tatar said Greek Cypriots that fled could reclaim their properties through the Immoveable Property Commission (IPC).
But the move provoked an immediate backlash from Greek Cypriots, who see it as a bid to pressure them into selling off their properties.
On Friday, the UN Security Council issued a presidential statement on the matter, approved by all 15 member states.
"The Security Council condemns the announcement by Turkish and Turkish Cypriot leaders on July 20, 2021, on the further reopening of a part of the fenced-off area of Varosha," it read.
"The Security Council expresses its deep regret regarding these unilateral actions that run contrary to its previous resolutions and statements."
It also called for "the immediate reversal of this course of action and the reversal of all steps taken on Varosha since October 2020”, citing the need to avoid any action that could "raise tensions on the island and harm prospects for a settlement”.
A 1984 UN Security Council resolution states that any attempt to settle any part of Varosha by people other than its inhabitants would be "inadmissible".
Varosha’s 15,000 Greek Cypriot residents fled in the face of advancing Turkish troops in 1974. The area was fenced off until last October when Turkish and Turkish Cypriot authorities first announced its “re-opening".
Some Turkish Cypriots have also condemned the move as undermining efforts at reconciliation between the two communities.
Numerous rounds of UN-mediated talks aimed at reuniting Cyprus have ended in failure, with the last push for a peace deal in July 2017 ending in acrimony.
UN Secretary-General Antonio Guterres held informal talks with Greek and Turkish Cypriot leaders in Geneva in April which also failed to make headway on the island’s future.
Both Turkey’s Erdogan and Turkish Cypriot leader Tatar have said a permanent peace in Cyprus can only come through the international community’s recognition of two separate states.