Migrant crisis: Merkel says EU must secure external borders
All EU countries must be prepared to send security staff to the bloc's external borders, German Chancellor Angela Merkel has said.
She said it would be unfair to ask EU countries seeing the majority of initial migrant entries to secure borders as well.
Mrs Merkel was speaking as she arrived at an EU leaders' summit in Brussels.
The meeting aims to secure Turkey's agreement to a plan to halt the flow of refugees trying to reach Europe.
Nearly 600,000 migrants have reached the EU by sea so far this year, many of them travelling from Turkey to Greece before seeking to head north.
"It's quite obvious that only a few countries today take the majority of refugees and if these countries now are asked to secure the external borders on top of that, I don't think it would be what we could call a fair distribution of effort," Mrs Merkel said.
She described the current situation as "very disorderly".
The summit aims to tackle the migration crisis by working with non-EU countries, protecting the EU's external borders and ensuring some migrants are sent back.
Estonia's Prime Minister Taavi Roivas said immediate action was needed to preserve the EU's borderless Schengen area, which has come under increasing pressure, with some states reintroducing controls to prevent migrants from crossing borders.
Meanwhile Hungary's Prime Minister Viktor Orban said his country would decide whether to close its border with Croatia by Friday.
Hungarian state TV reported Mr Orban as saying he would prefer the EU to defend its external border in Greece but could seal its Croatian border "within an hour if necessary".
There were also calls for member states to address the causes of migration by providing more money for Syrian refugees in Jordan, Lebanon and Turkey and for development in Africa.
"Member states need to put their money where their mouth is," said EU foreign policy chief Federica Mogherini.
Analysis: Ed Thomas, BBC News, Athens
More than 400,000 migrants and refugees have crossed the Aegean Sea this year, hundreds have drowned. But the seas are getting rougher and many in Greece are looking to EU leaders to find a solution.
One idea mentioned in Germany was for joint patrols by the Turkish and Greek coastguards. But all this received a loud and clear "no" from the Greek government.
Sovereignty is key. The message from Athens is that the islands of the Aegean belong to the Greeks and it is down to them to patrol the waters no-one else.
The fear in Athens is that if Turkey is allowed to patrol the waters around the Greek islands, boundaries will blur and Ankara will stake new claims to islands that sit close to the Turkish coast.
Instead Greece wants Turkey to patrol its shores better, and even stop migrants leaving in the first place.
In return Athens believes the EU should offer big financial incentives and rewards to Turkey so it can improve the accommodation and build more refugee camps.
The BBC's Matthew Price is sending social media broadcasts from Calais on the EU migration crisis. You can follow his reports here.
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Merkel under pressure: Chancellor's migrant policy faces criticism at home
Focus on Turkey: Why the EU views Syria's northern neighbour as key
Crisis in graphics: Migration numbers explained
BBC Europe correspondent Chris Morris says most EU leaders are convinced that efforts to contain the migration crisis will not succeed without closer co-operation with the Turkish government.
But, he adds, Ankara wants plenty in return. It is reportedly asking for €3bn in aid to ease the strain of hosting refugees, as well as visa liberalisation and progress on Turkey's stalled application for EU membership.
A German diplomat in Brussels told reporters negotiations between European Commission vice-president Frans Timmermans and Turkish officials in Ankara were "going in the right direction" but said there was still a long way to go.
EU sources say several countries - Greece, Cyprus and France among them - are cautious about rushing into an agreement with Turkey too quickly.
Discussions continued over dinner following the end of the first session, Mr Tusk's spokesman tweeted.
Turkey is hosting some two million migrants, most of them fleeing the war in neighbouring Syria.
Turkey has also called for the establishment of an international "safe zone" for refugees inside northern Syria - but Mr Tusk said Russia's involvement in Syria made the idea more difficult.
The 28 EU leaders meeting in Brussels are hoping the Turkish government will sign up to a joint action plan that includes:
- Financial and procedural aid for Turkey to deal with migrants
- Gaining permission from Turkey to help patrol its coastline
- Combating people smuggling
- Strengthening return operations