EU leaders are meeting with the prime minister of Turkey in Brussels in the hope of sealing a deal which would allow irregular migrants to the country to be returned after crossing the Mediterranean by boat.
A package agreed by leaders of EU member states on Thursday evening is believed to involve Europe taking in one Syrian refugee from camps in Turkey for every migrant returned from Greece, up to a limit of 72,000.
Arriving for talks with European Commission president Jean-Claude Juncker ahead of a meeting of all 28 leaders, Turkish PM Ahmet Davutoglu said he was hopeful of reaching an agreement which would help Syrian refugees and deepen ties between the EU and his country, whose long-standing application for membership is to be moved forward as part of the deal.
"Turkey has received 2.7 million refugees without any significant assistance from anywhere," said Mr Davutoglu.
"Today I want to re-emphasise that Turkey will continue her policy to have this attitude of a humanitarian perspective.
"The EU and Turkey have the same goal, the same objective, to help Syrian refugees especially and also to have a new future in our continent in a right manner.
"I am sure - I hope - we will be achieving our goal to help all the refugees as well as to deepen Turkey- EU relations, which is good news for our continent and for humanity altogether."
After talks between the 28 leaders over dinner which stretched late into the night, Luxembourg's PM Xavier Bettel tweeted that agreement had been reached on a settlement which could be put to Mr Davutoglu.
It is understood that Turkey stands to gain 6 billion euro (£4.7 billion) in EU aid - doubling the 3 billion offered late last year - to support refugees who have flooded into the country fleeing the civil war in neighbouring Syria. And its 75 million nationals could gain visa-free access to the EU's Schengen border-free area, which does not include the UK.
David Cameron stressed on Thursday that the deal would not involve Britain adding to the 20,000 Syrian refugees it has already agreed to take from camps in the region over five years.
He told fellow leaders he wanted to see more boats being turned back to the Turkish coast by the country's coastguard, working in co-operation with a Nato mission involving one Royal Navy ship. Britain is sending several more officers from the National Crime Agency to assist with border operations in Greece and Turkey.
Mr Cameron urged fellow leaders to work with the new Government of National Accord in Libya to extend an EU mission closer to the shore of the north African state, with the aim of deterring thousands of migrants from embarking on the perilous sea journey to Europe this summer.
The Prime Minister also announced he is extending the deployment of HMS Enterprise on anti-trafficking operations in the central Mediterranean at least until the summer, and wants to see the mission expanded into Libyan territorial waters to enhance its deterrent effect.
If a new deal with Turkey succeeds in cutting migration in the eastern Mediterranean, economic migrants may divert to the north African country as improving weather makes the crossing to Italy more viable during the summer months, he said.
Some 170,000 migrants arrived in Italy from Libya in 2014 and 150,000 last year, but the death toll was much higher than on the Turkish route because of the longer distances involved.
The EU's Operation Sophia is currently able to operate only in international waters, but has already detained 53 smugglers and destroyed 90 vessels - including 69 rubber dinghies, 20 wooden boats and one fishing vessel - since last July.
Some people-smugglers have been taking advantage of the fact that EU vessels cannot sail close to the Libyan coastline by taking boatloads of migrants to the edge of international waters before casting them loose.
As well as signalling his readiness to keep HMS Enterprise in the area if the Operation is extended beyond July, Mr Cameron said Britain is willing to deploy other assets.
He believes an EU naval presence close to the Libyan shore would deter many migrants from setting out and would allow local coastguards to escort other boats back to shore, where they can be destroyed.
The proposed deal with Turkey was denounced by the Refugee Council as "immoral, unworkable and probably illegal".
Amnesty International refugee director Steve Symonds said: "The plan lacks both logic and compassion. By abandoning their legal obligations, European leaders won't put a stop to refugee migration."
But Mr Cameron's official spokeswoman said the UK believes the proposed new arrangements with Turkey can be imposed "in line with EU and international law" as individual cases would be assessed on their merits.
Mr Juncker insisted any arrangements would respect both European law and the Geneva Conventions.
Dutch PM Mark Rutte suggested the prospect of immediate return from the Greek islands to Turkey would halt the flow of migrants by the eastern Mediterranean route "in three to four weeks" after finalisation of the deal.