EU President Donald Tusk warned Thursday that "difficult" talks lay ahead on a contentious plan being negotiated with Turkey to end irregular migration into Europe, hours before the bloc's leaders were set to meet to forge a common approach.
The plan - under which migrants would be swapped between the European Union and Turkey in a bid to end illegal smuggling across the Aegean Sea to Greece - is the bloc's latest effort to end a surge of migrants and asylum seekers into the continent.
Last year, more than 1 million people reached Europe's shores, with most of them travelling via Greece in the hope of reaching wealthy northern states such as Germany and Sweden. Many had fled the war in Syria, but economic migrants joined their ranks.
The EU now hopes that, together with Turkey, it can halt the flows, but the legally challenging plan has been lambasted by human rights activists and met with resistance from several EU capitals.
In particular, Turkish demands for progress on its long-running EU membership bid have been opposed by Cyprus, which is in the midst of delicate reunification talks with the Turkish-backed north of the island.
Tusk, who visited Nicosia and Ankara this week as part of his efforts to find consensus, said Thursday that he was "cautiously optimistic - but frankly speaking more cautious than optimistic" of finalizing the plan with Turkey this week.
The 28 EU leaders will discuss the deal late Thursday, before meeting with Turkish Prime Minister Ahmet Davutoglu on Friday.
Tusk stressed three key principles, noting that the plan must be "acceptable to all 28 member states, no matter big or small;" must "fully comply with EU and international law," and must "effectively help to solve the migration crisis."
"We are moving into difficult talks," he said. "Only if we all work together in a coordinated measure and keep our cool will we achieve success."