EU President Donald Tusk warned Thursday that "difficult" talks lay ahead on a contentious plan being negotiated with Turkey to stem migration flows 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 Turkey to 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 its leaders, together with Turkey, can declare an end to the flows. But the legally challenging deal being considered by the two sides has been lambasted by human rights activists and met with resistance from several EU capitals.
The EU won some backing on Thursday, however, from Europe's leading human rights watchdog.
The Strasbourg-based Council of Europe welcomed the fact that, as part of the migrant-swapping deal, the EU intends to fully process asylum requests for those arriving on Greek islands before deciding whether to send them back to Turkey.
"It is extremely important that every application for asylum should be treated individually and there should be no question of 'blanket' returns," its leader, Thorbjorn Jagland, said. "I hope that these principles will prevail during the negotiations starting today."
But others remain sceptical. The German refugee aid organization Pro Asyl said it is a "farce" to expect Greece to adequately process applications when it has a "de facto non-existent asylum system."
"These fig-leaf procedures won't hide Europe's guilty conscience if large-scale returns of refugees start happening now," added John Dalhuisen of the Amnesty International human rights group, which was staging a protest Thursday outside the leaders' summit venue.
Thousands of people also took to the streets of Spain on Wednesday evening, calling the planned deal a "disgrace." All the political parties in the Spanish parliament have agreed on the need to reject the pact with Turkey.
"The refugees are fleeing from terror and war and cannot here come upon a wall of indifference, a wall of European denial," Socialist leader Pedro Sanchez said this week.
Cyprus is considered to be another potential stumbling block. The island, which is in the midst of delicate reunification talks with its Turkish-backed north, has been resisting Ankara's demands for quick progress on its long-running EU membership bid.
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.
"We are in talks with Cyprus, with Turkey, with Greece to work out an amicable solution," European Commission President Jean-Claude Juncker added later in the day.
In an interview with Germany's Handelsblatt newspaper, Juncker said that Turkey is not ready for EU membership and "I believe it still won't be ready in 10 years."
The 28 EU leaders will meet with Turkish Prime Minister Ahmet Davutoglu on Friday, after discussing the migration deal amongst themselves on Thursday evening.
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."