(CNN) Turkey and the European Union have reached agreement on key points of a proposal to handle the overflow of refugees, according to a tweet for the spokesman of European Commission President Jean-Claude Juncker.

"Deal. Breakthrough with Turkey," read the tweet from Martin Selmayr.

The proposal still needs formal approval. The next step is for the proposal to be taken to EU leaders at the European Council migration crisis meeting scheduled for March 17-18.

"President of #EUCO will take forward the proposals and work out the details with the Turkish side before the March #EUCO," read a tweet from Xavier Bettel, the Prime Minister of Luxembourg.

"We agreed to work on the basis of 6 principles," he tweeted. Those principles were later spelled out in a statement from the European Council. They are as follows:

"To return all new irregular migrants crossing from Turkey into the Greek islands with the costs covered by the EU;

"To resettle, for every Syrian readmitted by Turkey from Greek islands, another Syrian from Turkey to the EU Member States, within the framework of the existing commitments;

"To accelerate the implementation of the visa liberalization roadmap with all Member States with a view to lifting the visa requirements for Turkish citizens at the latest by the end of June 2016;

"To speed up the disbursement of the initially allocated €3 billion to ensure funding of a first set of projects before the end of March and decide on additional funding for the Refugee Facility for Syrians;

"To prepare for the decision on the opening of new chapters in the accession negotiations as soon as possible, building on the October 2015 European Council conclusions;

"To work with Turkey in any joint endeavour to improve humanitarian conditions inside Syria which would allow for the local population and refugees to live in areas which will be more safe."

Donald Tusk, president of the European Council -- as the group of 28 EU leaders is known -- said the key outcome of all the steps being taken to deal with the refugee crisis was this message: "The days of irregular migration to Europe are over."

Photos: Europe's migration crisis in 25 photos A woman cries after being rescued in the Mediterranean Sea about 15 miles north of Sabratha, Libya, on July 25, 2017. More than 6,600 migrants and refugees entered Europe by sea in January 2018, according to the UN migration agency , and more than 240 people died on the Mediterranean Sea during that month. Hide Caption 1 of 26 Photos: Europe's migration crisis in 25 photos Refugees and migrants get off a fishing boat at the Greek island of Lesbos after crossing the Aegean Sea from Turkey in October 2015. Hide Caption 2 of 26 Photos: Europe's migration crisis in 25 photos Hide Caption 3 of 26 Photos: Europe's migration crisis in 25 photos Migrants step over dead bodies while being rescued in the Mediterranean Sea, off the coast of Libya in October 2016. Agence France-Presse photographer Aris Messinis was on a Spanish rescue boat that encountered several crowded migrant boats. Messinis said the rescuers counted 29 dead bodies -- 10 men and 19 women, all between 20 and 30 years old. "I've (seen) in my career a lot of death," he said. "I cover war zones, conflict and everything. I see a lot of death and suffering, but this is something different. Completely different." Hide Caption 4 of 26 Photos: Europe's migration crisis in 25 photos Authorities stand near the body of 2-year-old Alan Kurdi on the shore of Bodrum, Turkey, in September 2015. Alan, his brother and their mother drowned while fleeing Syria. This photo was shared around the world, often with a Turkish hashtag that means "Flotsam of Humanity." Hide Caption 5 of 26 Photos: Europe's migration crisis in 25 photos Migrants board a train at Keleti station in Budapest, Hungary, after the station was reopened in September 2015. Hide Caption 6 of 26 Photos: Europe's migration crisis in 25 photos Children cry as migrants in Greece try to break through a police cordon to cross into Macedonia in August 2015. Thousands of migrants -- most of them fleeing Syria's bitter conflict -- were stranded in a no-man's land on the border. Hide Caption 7 of 26 Photos: Europe's migration crisis in 25 photos The Kusadasi Ilgun, a sunken 20-foot boat, lies in waters off the Greek island of Samos in November 2016. Hide Caption 8 of 26 Photos: Europe's migration crisis in 25 photos Migrants bathe outside near a makeshift shelter in an abandoned warehouse in Subotica, Serbia, in January 2017. Hide Caption 9 of 26 Photos: Europe's migration crisis in 25 photos A police officer in Calais, France, tries to prevent migrants from heading for the Channel Tunnel to England in June 2015. Hide Caption 10 of 26 Photos: Europe's migration crisis in 25 photos A migrant walks past a burning shack in the southern part of the "Jungle" migrant camp in Calais, France, in March 2016. Part of the camp was being demolished -- and the inhabitants relocated -- in response to unsanitary conditions at the site. Hide Caption 11 of 26 Photos: Europe's migration crisis in 25 photos Migrants stumble as they cross a river north of Idomeni, Greece, attempting to reach Macedonia on a route that would bypass the border-control fence in March 2016. Hide Caption 12 of 26 Photos: Europe's migration crisis in 25 photos In September 2015, an excavator dumps life vests that were previously used by migrants on the Greek island of Lesbos. Hide Caption 13 of 26 Photos: Europe's migration crisis in 25 photos The Turkish coast guard helps refugees near Aydin, Turkey, after their boat toppled en route to Greece in January 2016. Hide Caption 14 of 26 Photos: Europe's migration crisis in 25 photos A woman sits with children around a fire at the northern Greek border point of Idomeni in March 2016. Hide Caption 15 of 26 Photos: Europe's migration crisis in 25 photos A column of migrants moves along a path between farm fields in Rigonce, Slovenia, in October 2015. Hide Caption 16 of 26 Photos: Europe's migration crisis in 25 photos A ship crowded with migrants flips onto its side in May 2016 as an Italian navy ship approaches off the coach of Libya. Passengers had rushed to the port side, a shift in weight that proved too much. Five people died and more than 500 were rescued. Hide Caption 17 of 26 Photos: Europe's migration crisis in 25 photos Refugees break through a barbed-wire fence on the Greece-Macedonia border in February 2016, as tensions boiled over regarding new travel restrictions into Europe. Hide Caption 18 of 26 Photos: Europe's migration crisis in 25 photos Policemen try to disperse hundreds of migrants by spraying them with fire extinguishers during a registration procedure in Kos, Greece, in August 2015. Hide Caption 19 of 26 Photos: Europe's migration crisis in 25 photos A member of the humanitarian organization Sea-Watch holds a migrant baby who drowned following the capsizing of a boat off Libya in May 2016. Hide Caption 20 of 26 Photos: Europe's migration crisis in 25 photos A migrant in Gevgelija, Macedonia, tries to sneak onto a train bound for Serbia in August 2015. Hide Caption 21 of 26 Photos: Europe's migration crisis in 25 photos Migrants, most of them from Eritrea, jump into the Mediterranean from a crowded wooden boat during a rescue operation about 13 miles north of Sabratha, Libya, in August 2016. Hide Caption 22 of 26 Photos: Europe's migration crisis in 25 photos Refugees rescued off the Libyan coast get their first sight of Sardinia as they sail in the Mediterranean Sea toward Cagliari, Italy, in September 2015. Hide Caption 23 of 26 Photos: Europe's migration crisis in 25 photos Local residents and rescue workers help migrants from the sea after a boat carrying them sank off the island of Rhodes, Greece, in April 2015. Hide Caption 24 of 26 Photos: Europe's migration crisis in 25 photos Investigators in Burgenland, Austria, inspect an abandoned truck that contained the bodies of refugees who died of suffocation in August 2015. The 71 victims -- most likely fleeing war-ravaged Syria -- were 60 men, eight women and three children. Hide Caption 25 of 26 Photos: Europe's migration crisis in 25 photos Syrian refugees sleep on the floor of a train car taking them from Macedonia to the Serbian border in August 2015. How to help the ongoing migrant crisis Hide Caption 26 of 26

The news came as European Union leaders held an emergency summit Monday with Turkey aimed at staunching the flow of migrants to Europe as they search for a solution to the continent's worst refugee crisis since World War II.

About 134,900 migrants have crossed the Mediterranean Sea to Europe so far this year, the International Organization for Migration said, with more than 400 having died making the dangerous journey.

The vast majority of the migrants have come via Turkey.

EU heads of government were expected to push Turkey to do more to prevent migrants from leaving its shores, by targeting human trafficking networks and repatriating so-called economic migrants -- people who have left their homelands in hopes of a better life, rather than out of fear for their lives.

In return, the EU will support Turkey in managing the millions of refugees the country has already taken in. It already hosts 2.6 million migrants.

Under a joint action plan agreed upon last year, the EU agreed to pay Turkey €3 billion ($3.3 billion) to support its refugee population and target people-smuggling networks -- a mission that has seen NATO warships deployed to the eastern Mediterranean this year.

Turkish PM: 'Solidarity' only answer

Ahead of the summit in Brussels, Belgium, British Prime Minister David Cameron said in a statement that his priorities would be "breaking the link between getting on a boat and getting resettlement in Europe."

He proposed doing so by smashing trafficking gangs and stepping up the return of economic migrants, supporting Turkey and providing technical assistance to Greece to speed up the processing of migrant claims and repatriation of illegal migrants.

Also before the summit Monday, Turkish Prime Minister Ahmet Davutoglu said, "The only way to respond to this challenge is solidarity.

"At the end of the day, our continent is our continent altogether," he told reporters in Brussels.

The International Rescue Committee lauded the meeting Monday but warned that "closing all of Europe's borders without offering alternative routes to safety will not work."

"In fact," the humanitarian organization said, "the only winners will be the smugglers, as people take more elaborate and more dangerous routes to safety."

Expert: Russia exploiting crisis

The summit comes as a desperate bottleneck of more than 10,000 people swells at the Greece-Macedonia border, and a senior NATO expert on strategic communications warned that a belligerent Russia was attempting to stir up emotions in Europe over the migrant influx.

NATO's Janis Sarts told CNN that Moscow appeared to be conducting an information war over the refugee issue, drumming up public anger to its own political ends.

"What we have seen is a lot of strong evidence to suggest that by deliberately distorting facts through their centrally controlled media, Russia is exploiting contentious issues in order to undermine European democratic values such as freedom of speech, tolerance and human rights," said Sarts, director of the NATO Strategic Communications Center of Excellence based in Riga, Latvia.

"Russia's political establishment has had no reservations about capitalizing on a potentially divisive issue such as refugees with a view to interfering in legitimate democratic processes outside of its own borders."

Buildup of migrants grows in Greece

Meanwhile, a major backlog of about 35,000 migrants has built up in Greece, a country already struggling under the weight of a debt crisis, following a decision by eight countries along the main overland migration route to Western Europe to all but close their borders in response.

Greece is the entry point into Europe for the overwhelming majority of the migrants, with arrivals averaging 1,800 a day last month.

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On Monday morning, CNN's Arwa Damon reported from at a migrant camp at Idomeni, a village on the Greek border with Macedonia. Doctors without Borders said more than 11,000 people are crammed into the camp, which was designed as a transit camp for 1,500.

Authorities are letting only a few hundred Syrians and Iraqis through to Macedonia each day, raising fears that Greece is at risk of becoming a mass refugee camp.

Damon said those taking shelter in tents at Idomeni told her they hoped the Brussels meeting could result in the borders opening. But the reality is that there have been more barriers built than removed in the past six months.

Many said they had already experienced the effects of Ankara's efforts to crack down on migrants on the Turkish coastline, with some reporting having been turned back multiple times before they eventually made it across the Aegean Sea to Greece.

The Aegean, a stretch of the Mediterranean separating Turkey and Greece, is the main route that traffickers use to bring migrants into Europe.

Twenty-five migrants died in its waters Sunday in an attempt to reach Greece when their boat capsized off of Turkey's western coast, Turkey's semiofficial Anadolu news agency reported.

Consensus on crisis?

Last month, ministers from countries along the main Balkan migration route through Europe -- including Macedonia, Serbia, Croatia and Slovenia -- agreed to tighten border controls to slow arrivals to a trickle.

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That response, which undermined pledges to present a united European front to the crisis and share the migrant burden, was criticized by international organizations, with the U.N. refugee agency warning last week that Europe now faced an "imminent humanitarian crisis, largely of its own making."

Arriving at the Brussels summit Monday, Greek Prime Minister Alexis Tsipras stressed it was a common European problem: "So we have to find collective, European solutions."

Unfortunately, since the previous summit on the crisis, "there were agreements that didn't implement for everybody," he said, apparently referring to restrictions along the Balkan migration route.

He said he looked forward to "substantial results" from the meeting on decreasing migrant flows, breaking trafficking networks and accelerating efforts to relocate asylum seekers throughout EU countries.

EU leaders agreed last year to accept 160,000 refugees among its member states, but so far less than 1,000 have been processed.

UK military steps in

Britain has deployed the landing ship dock RFA Mounts Bay , two cutters and a Wildcat helicopter to the Aegean Sea as part of stepped-up NATO efforts to stop smugglers and stem the flow of migrants, the British Prime Minister announced Monday.

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Cameron described the migration crisis as "the greatest challenge facing Europe today."

The RFA Mounts Bay will join ships from Canada, Germany, Turkey and Greece on patrol.

They will participate in an operation aimed at reducing the flow of migrants from Turkey by spotting smugglers and sharing information with the Turkish coast guard, Cameron's statement said. From there, it's up to the Turkish coast guard to determine whether to turn smugglers' boats around.

"We've got to break the business model of the criminal smugglers and stop the desperate flow of people crammed into makeshift vessels from embarking on a fruitless and perilous journey," Cameron said.

British Defense Secretary Michael Fallon said that as well as surveillance and life-saving duties, the vessel was part of a mission "that aims to return migrants to Turkey rather than taking them on to the EU

"That will disrupt the business model of the criminal gangs encouraging people to risk their lives by making these dangerous journeys," he said.

NATO Secretary-General Jens Stoltenberg announced Sunday that the anti-trafficking operation in the Aegean had been expanded into Greek and Turkish territorial waters as well.