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The EU will significantly toughen its borders against migrants trying to get to Europe under a new deal agreed by leaders today.
Thousands of people arriving by boat the Greek islands will be sent back to Turkey from Sunday.
Video report by ITV News deputy political editor Chris Ship.
Donald Tusk, the president of the European Council, hailed the deal after complex negotiations, but warned it was no "silver bullet".
"The reality is more complex," he added.
More than 1,700 migrants and a number of smugglers have been detained near Turkey's Aegean coast.
Some 1,734 migrants and 16 smugglers were detained in the operation launched near the town of Dikili, in Izmir province on Turkey's Aegean coast.
The operation, aimed at stopping refugees reaching the Greek island of Lesbos, involved the coastguard, navy and police and was backed by air support, the military said in a statement
It comes as Turkey secured a deal with EU leaders aimed at discouraging migrants from travelling from Turkey to Greece.
Turkey has hailed an agreement with Europe to help ease the migrant crisis as a "historic day."
Under the Brussels deal, refugees and migrants making the dangerous crossing from Turkey to Greece after Sunday will be returned and placed in a camp. It effectively closes Europe's border.
In return, the EU will take in thousands of Syrian refugees directly from Turkey and reward it with more money, early visa-free travel and faster progress in EU membership talks.
Migrants who arrive in Greece from Sunday will be subject to being sent back once they have been registered and their individual asylum claim processed.
The returns are to begin on April 4, as would resettlement of Syrian refugees in Europe
ITV News Deputy Political Editor Chris Ship reports:
Greece's capacity to receive people and assess asylum claims must be strengthened for the deal between the EU and Turkey to work, the United Nations has said.
It also said Turkey must give a fair and timely review to those needing protection.
In a statement, the UN High Commissioner for Refugees (UNHCR) said applicants in Greece should have "the right to appeal before any readmission to Turkey".
German Chancellor Angela Merkel said an EU-Turkey deal to halt illegal migration to Europe was bound to run into setbacks and faced big legal challenges but nevertheless had an "irreversible momentum".
Merkel voiced satisfaction but also caution at a news conference after the deal was agreed.
She said: "I have no illusions that what we agreed today will be accompanied by further setbacks. There are big legal challenges that we must now overcome.
"But I think we've reached an agreement that has an irreversible momentum and it was very important for me that we managed to agree all that among the 28 today."
President of the European Parliament Martin Schulz has welcomed the EU deal with Turkey aimed at easing the migrant crisis.
He called for all parties to implement measures agreed under the deal "swiftly" and to fully respect all conditions agreed.
"This is a historic day," Turkish prime minister Ahmet Davutoglu said after a EU deal with Turkey aimed at easing the migration crisis.
Under the terms of the agreement, Greece is to start returning migrants arriving by boat from Turkey from Sunday.
All migrants arriving in Greece from Sunday will be returned to Turkey, Donald Tusk has said.
Speaking at a press conference, he said the deal will be implemented "gradually" based on a 1-for-1 principle.
David Cameron has welcomed an EU deal with Turkey, which he said could "significantly" reduce numbers of migrants crossing the eastern Mediterranean to enter Greece by boat.
The Prime Minister said the arrangement was "a plan to break the link between getting on a boat and getting settlement in Europe.... a plan to bust the business model of the smugglers".
He added: "For the first time in this crisis, I believe we have a plan that, properly and fully implemented, could make a difference."
The European Union and Turkey have sealed a deal to return migrants arriving across the Aegean to Europe, Lithuanian President Dalia Grybauskaite said on Twitter.
She said a "test of implementation" is due to start on Sunday.
Latest ITV News reports
The agreement involves closing the EU border on March 20 and sending back migrants who arrive in Greece after that date to Turkey.
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