European Union leaders and Turkey are meeting in Brussels in the hopes of clinching a deal to end the migrant crisis.
After daylong talks that ended early on March 18 in Brussels, EU leaders agreed to offer Turkey financial and political concessions if it stops migrants from reaching Greece.
Turkish Prime Minister Ahmet Davutoglu said he was hopeful it would be possible to find common ground with the EU.
"EU and Turkey we have the same goal, the same objective, to help Syrian refugees especially and also to have a new future in our continent in a bright manner," Davutoglu said as he arrived for the summit in Brussels on March 18.
But Davutoglu warned EU leaders Ankara's offer to curb the refugee flow to Europe was strictly a humanitarian rather than a "bargaining" issue.
"For Turkey, the refugee issue is not an issue of bargaining but an issue of values, humanitarian values as well as European values," Davutoglu said.
EU leaders gave chief negotiator EU President Donald Tusk a mandate to conclude an accord with Turkey to take back all migrants who cross the Aegean Sea to Greece.
In return, the EU would take in Syrian refugees directly from Turkey, provide up to 6 billion euros ($6.6 billion) in aid to support housing refugees there, and speed up Ankara's EU membership negotiations and visa-free travel plans.
Under the deal, officials said the EU would pay to send new migrants arriving in Greece who don't qualify for asylum back to Turkey. For every migrant returned, the EU would accept one Syrian refugee, up to a total of 72,000 people to be distributed among European states.
WATCH: The Turkish coast guard stop a group of Syrians from reaching Greece by boat on March 18.
German Chancellor Angela Merkel, who first devised the plan with Davutoglu at a summit 10 days ago, said finalizing the deal would not be easy but all European leaders want an agreement to slow or stop the arrival of thousands of migrants a day on Greek islands.
Since January 2015, a million migrants and refugees have entered the EU by boat from Turkey to Greece, and more than 132,000 have arrived this year alone.
Much of the debate within the EU, Merkel said, has focused on addressing criticisms by human rights groups about returning migrants to Turkey, a country with a patchy and worsening rights record.
Lithuanian President Dalia Grybauskaite said before the late-night agreement that the plan was "very much on the edge of international law" because of a lack of guarantees for the rights of migrants and asylum-seekers left in Turkey.
Drafts of the plan show that the EU is demanding that Turkey adopt legislation to protect asylum seekers in line with the Geneva Convention, though Ankara has limited its formal commitments to that treaty in the past.
With the offer in hand, Tusk planned to lead a negotiating team meeting with Davutoglu on the morning of March 18.
Securing Turkey's agreement is far from certain. Davutoglu warned on his way to Brussels that that he would not accept a deal to "turn Turkey into an open prison for migrants."
The whole deal also risks being derailed by disputes over Turkey's negotiations to join the EU, particularly a long-running conflict between Cyprus and Turkey, which does not recognize the Greek Cypriot government.
Cypriot President Nicos Anastasiades said it could use its veto to block an accord if Ankara did not give Cyprus the same rights as other EU states to access Turkish ports and airports.
Because of these lingering, complicated disputes, the EU is offering only to "prepare for a decision" on opening new accession chapters for Turkey "as soon as possible," a vague offer that may offend Turkey, officials said.
EU officials argue that the alternative to holding people back in Turkey is to see a further build-up of migrants stranded in increasingly dire conditions in Greece. Already an estimated 40,000 people are marooned on the Greek side of the border with Macedonia after Balkan countries slammed their borders shut to migrants last week.
While the plan seeks to preserve the rights of asylum-seekers to legal protections, EU officials stress that the overall goal is to quickly deter most people from even trying to cross the Aegean Sea to Greece, putting an end to the steady stream of migrants seen in the last year.