EU to hold migrant summit with Turkey in early March

"Our joint action plan with Turkey remains a priority, and we must do all we can to succeed," he said.

All 28 EU states will attend. An invitation has yet to be sent to Turkey's prime minister Ahmet Davutoglu, but once confirmed, the date will be set.

Tusk's announcement comes after a mini-summit with Davutoglu at the Austrian embassy in Brussels was cancelled due the bombing in Ankara on Wednesday.

The planned meeting points to the large importance Ankara plays in the EU's strategy to control and manage a migrant crisis that has so far proven hard to manage.

Efforts to stem the flows have increasingly relied on border control measures that risk ring-fencing Greece.

Tusk made the Turkey announcement at an EU summit devoted to migration and the EU-UK negotiations. Officials had initially expected the migration part to be over quickly, but it dragged out late into the night.

"It's been a very long debate on migration," said one tired EU diplomat.

The leaders debated outstanding issues in EU-level policies on migration, which have yet to fully deliver.

Only around 500 people have been relocated from Greece and Italy in a scheme, launched last September, meant to distribute 160,000 over a two-year period.

Greece has four of five of its so-called hotspots, screening zones for arrivals, up and running.

Nervosity

Meanwhile, a move by Austria to cap the number of daily arrivals and asylum seeker registrations to 80 has provoked fears of bottlenecks along the Western Balkan route.

Despite sharp criticism from the EU-executive over the plan, the cap will remain in place.

One EU head of government told reporters it had contributed to the "nervousness” of the debates, but added: "Nobody wants to clash with Austria.”

“[German leader] Merkel did not jump on [Austrin chancellor] Faymann … to slit his throat," he said.

The German chancellor played down any split over the issue with Austria despite diverging national policies on how to best handle the crisis. But she noted Vienna's decision had come as a surprise.

"We had an exchange of views, but not a heated debate with Austria. It has made matters more urgent for us to see whether we are on the right track or whether we ought to adopt alternative measures," she said.

The conclusions issued by the summit place an emphasis on "rapidly" stemming the flows, protecting external borders, reducing irregular migration, and protecting the passport-free Schengen zone.

It also backs Nato's efforts to assist in the "reconnaissance, monitoring, and surveillance of illegal crossings" in the Aegean Sea between Turkey and the Greek islands.

Turkey is seen as a central pillar to EU ambitions, with all EU leaders saying the deal with Ankara agreed last year - to reduce flows in return for €3 billion and political concessions - "remains a priority".

A large chunk of the money is set to go to humanitarian aid and access to education for refugee children in Turkey. Summit leaders also want Ankara to speed up labour market access to Syrian refugees and step up data sharing with the EU.

"Once the flow is reduced, legal resettlement on voluntary basis is something we are going to look into, all 28 supported this," said Merkel.