Leaders of the European Union (EU) will meet in Brussels on Thursday to agree on a deal to offer Turkey the following day that would secure Ankara's commitment to a scheme intended to halt the flow of refugees to the Greek islands.
A year into a crisis in which more than a million people have arrived in chaotic misery, many of them Syrian war refugees most of whom have come from Turkey through Greece to Germany with dangerous sea crossings and long treks, hopes have risen around the summit table that they may have found a way to at least slow the movement.
"Work is progressing but there is still a lot to do," European Council President Donald Tusk wrote to leaders, inviting them to the summit he will chair. After discussing the economy, the 28 EU national leaders will discuss the refugee crisis over dinner, starting around 8 pm (1900 GMT).
A breakfast is set for Friday with Turkish Prime Minister Ahmet Davutoglu, where Tusk hopes to finalise a deal which Davutoglu first sprang on the EU with backing from German Chancellor Angela Merkel at a special summit 10 days ago.
Under the deal, which was set out in fuller fashion by Tusk in a draft for EU leaders on Wednesday, Turkey will - in addition to a previous agreement to try and prevent the smuggling of refugees on rafts - take back all those refugees, including Syrians, who make it to the Greek islands off Turkey's coast.
The draft says the plan is "to break the business model of the smugglers and to offer migrants an alternative to putting their lives at risk."
It stresses the plan is "a temporary and extraordinary measure which is necessary to end the human suffering and restore public order."
Cyprus question overshadowing refugee deal
Potentially the most explosive topic - which diplomats say risks derailing the whole deal - will be how Davutoglu responds to a vague offer to open new "chapters" of Turkey's negotiations to join the EU at some distant future date.
As an EU member, the Greek Cypriot administration has previously frozen a number of negotiation "chapters" concerning Ankara’s EU membership on the grounds that Turkey has not yet opened its ports and airports to Greek Cypriot traffic.
Greek Cypriots have been at loggerheads with Turkey since 1974, when the island was divided into two spheres, the south being governed by the Greek Cypriot administration and the north being governed by the Turkish Cypriots.
In July 1974, the Turkish government militarily intervened in the northern part of the island with the intention of protecting the Turkish population after a short-lived Greek-orchestrated coup on the island aimed at union with Greece (a concept known in Greek as Enosis).
The island became independent in 1960 as the Republic of Cyprus. Three countries, Turkey, Greece, and Britain, were made its guarantor states, according to the Zurich and London agreements.
Following the establishment of the Republic of Cyprus many disagreements emerged between the island's diverse population of Greeks and Turks, particularly due to the failure of Greek Cypriot lawmakers to establish separate municipalities for Turkish Cypriots as outlined in the country's constitution.
Peace talks to resolve the Cyprus issue are now underway between the Greek and Turkish Cypriot sides, but Turkey - which maintains more than 30,000 troops in the Turkish Republic of Northern Cyprus since 1974 - is instrumental to any peace accord.
Greek Cypriot leader Nicos Anastasiades said on Tuesday, after a meeting with EU Council President, Donald Tusk, that he conveyed that his administration "does not intend to consent to the opening of any chapters if Turkey does not fulfil its obligations as described in the negotiating framework."
The EU must not allow the "caprice" of Greek Cypriots to spoil a planned refugee deal with Turkey, the Turkish EU Minister, Volkan Bozkir, said on Wednesday, after Greek Cypriots vowed to block efforts to speed up Ankara's accession talks.
"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," Bozkir underlined.
Tusk's draft says the EU would work with Turkey to "prepare for a decision" on opening new accession chapters "as soon as possible" - a hazy prospect Davutoglu may not appreciate.
Furthermore, in his invitation letter, Tusk stressed that only if the refugee deal could help advance the broader talks on ending the long confrontation concerning the Cyprus issue, could it hope to succeed.
Legal hurdles and growing disagreements
To satisfy EU and international law, Greece and Turkey will have to modify domestic legislation so that Turkey is regarded as protecting asylum seekers in line with the Geneva Convention, even though Ankara limits its formal commitments to that treaty.
EU officials argue that the alternative to holding people back in Turkey is to see a further build-up of refugees stranded in deteriorating conditions in Greece, whose European neighbours have closed their borders. Already over 40,000 are marooned.
Legal gymnastics, and the scorn of UN and other rights bodies aside, the deal foresees all those arriving having a right to state their case for asylum and to appeal.
However, EU officials stress that the intention is quickly to deter most people from even trying to make the crossing, so the arrival of thousands a day as occurred last year is unlikely. If such numbers keep coming, the plan will have failed, they say.
For each Syrian refugee who eludes efforts to stop refugee flow whom Turkey agrees to take back, Turkey will see a Syrian refugee resettled directly to Europe. The draft makes clear the total number is likely to be limited to about 72,000 out of nearly 3 million Syrians in Turkey.
That figure represents what the deeply divided EU states agreed last year to take in under two different schemes for sharing responsibilities. Leaders may talk more about who takes how many. Tusk's draft spoke of the process being "voluntary" in a nod to eastern EU states which oppose a series of refugees quotas Brussels imposed last year.
Longer-term, the EU leadership and the likes of Merkel are pushing hard for a system of resettling much larger numbers of refugees from the Middle East in Europe. That is opposed by others who say it would fuel xenophobic nationalism which has already surged, as seen in elections on Sunday in Germany.
Diplomats said there was also likely to be discussion of how quickly a second 3-billion-euro tranche of aid for Syrians in Turkey should be on the table for Davutoglu and of the precise details of an offer to provide visa-free travel to Europe for Turks by late June, if Ankara meets numerous conditions in time.