Refugees and migrants at a makeshift camp near the village of Idomeni, Greece, March 17

ANKARA — European Union leaders agreed to offer Turkey financial and political concessions if it stops migrants reaching Greece and will meet the Turkish prime minister in Brussels on Friday to try and clinch the deal.

Even if they can overcome possible objections from Ahmet Davutoglu, however, Thursday’s EU summit revealed considerable doubts among the Europeans themselves over whether the deal can be made either legal in international law or workable.

After talks over dinner, leaders gave negotiators a mandate to conclude an accord with Turkey by which it would take back all migrants who reach Greek islands off its coast; in return the EU would take in Syrian refugees direct from Turkey, give aid for Syrians there, speed Ankara’s EU membership negotiations and a scheme to let Turks visit Europe without visas.

German Chancellor Angela Merkel, who first devised the plan with Davutoglu and sprang it on surprised peers at a special summit 10 days ago, said a deal would not be easy but that all the European leaders wanted an agreement to slow the arrivals.

Much of the debate on Thursday, she said, focused on ensuring that a plan which has outraged human rights agencies could ensure that those returned to Turkey, a country with a patchy and worsening rights record, would have asylum rights protected.

Summit chairman Donald Tusk would lead a negotiating team to meet Davutoglu on Friday morning to prepare a lunch involving all 28 EU national leaders with the Turkish premier.

“An agreement with Turkey cannot be a blank check,” Belgian Prime Minister Charles Michel warned, echoing many colleagues who face complaints that Europe is selling out to anti-immigrant nationalists at home by outsourcing its problems to the Turks.

A major problem is Turkey’s four-decade-old dispute with EU member Cyprus, whose Ppesident, Nicos Anastasiades, insisted there could be no agreement to speed up Turkey’s EU membership talks until Ankara stops barring Cyprus from its sea and airports – itself a result of a refusal to recognize the Cypriot state.