The European Union has warned a deal with Turkey to curb mass migration to Europe hinges on the Turkish government acting to support peace talks in Cyprus.
European Council president Donald Tusk, chairing an EU summit, says much remains to be done to reach an agreement with Turkey.
Under a draft deal reached last week, Turkey would take back all migrants and refugees who enter the European Union from its shores or are detained in its territorial waters.
In return, it would receive more money, faster visa-free travel for Turkish citizens and an acceleration of its EU membership negotiations.
Turkey hopes the agreement can be signed off on at the EU summit in Brussels.
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European Commission first vice president Frans Timmermans says Turkey is not getting something for nothing.
"We're certainly not giving Turkey a free ride. Visa liberalisation for Turkish citizens rests on the fulfillment of clear conditions."
A stand-off with Cyprus could yet sink the deal.
The EU member has promised to block efforts to accelerate accession talks unless Turkey meets its obligations to recognise it as a state.
Cyprus and Turkey have been involved in a dispute since a 1974 Turkish invasion of the island.
Turkey's EU minister, Volkan Bozkir, says the bloc should not let the draft deal be marred by Cyprus.
"When a step has been taken towards a solution, when agreement has been reached on a package, the whole structure should not be allowed to be ruined just because of the caprice of one EU member country. The European Union must convince the Greek-Cypriot administration. If this package goes void because of this, the responsibility will be put on the shoulders of the Greek Cypriot administration."
In a letter to EU leaders, European Council president Donald Tusk has said the deal can only move forward if Turkey supports settlement talks in Cyprus.
German chancellor Angela Merkel is pushing for the deal on the migrants and refugees.
She says it would destroy the business of people smugglers.
"Instead, there would be a legal alternative, which would be safe for refugees and controllable for Europe. But since it's our goal to very quickly stop this illegality, this proposal will later be extended by voluntary quotas from EU member countries to take in Syrian refugees."
The proposal that EU member countries accept quotas of refugees has been rejected by several central European states.
