Turkey and the European Union struck a deal on Friday to stop the torrent of migrants crossing the Aegean Sea, declaring that those arriving on Greek shores can expect to be returned to Turkey beginning on March 20.
The plan is the EU's latest effort to end an unrestrained surge of migrants and asylum seekers that saw more than 1 million people reach European shores last year. Most crossed by sea from Turkey into Greece, aiming to then move on to wealthy northern countries.
Friday's deal hinges on a provision under which up to 72,000 Syrian asylum seekers will be returned from Greece back to Turkey. The EU argues that the move, which has been condemned by human rights groups, is key to undercutting migrant smuggling networks in the Aegean.
In exchange, the EU has agreed to resettle up to 72,000 Syrian asylum seekers out of Turkey. The new, one-for-one resettlement scheme will come to an end if this threshold is exceeded.
In return for its help, Ankara stands to receive new refugee aid and closer ties to the EU.
"We today realized that Turkey and the EU have the same destiny, the same challenges and the same future," said Turkish Prime Minister Ahmet Davutoglu, calling it an "historic day."
German Chancellor Angela Merkel said the message was that "whoever embarks on this dangerous route not only risks their life, but also has no chance of success." The aim was to end the "inhuman" smuggling of migrants and secure Europe's external borders, she added.
But the Amnesty International advocacy group slammed the deal as a "historic blow" to human rights, arguing that Turkey is not a safe country for refugees or migrants.
"Promises to respect international and European law appear suspiciously like sugar-coating the cyanide pill that refugee protection in Europe has just been forced to swallow," said John Dalhuisen of the group.
The UN Refugee Agency, which has been enlisted to help with the deal, warned that how it is implemented would be "crucial."
"The response must be about addressing the compelling needs of individuals fleeing war and persecution. Refugees need protection, not rejection," the organization said.
European Commission President Jean-Claude Juncker said the bloc now stood before a "Herculean task" in its aim of carrying out the deal in economically-embattled Greece.
An overall 4,000 officials would be needed there to help process new arrivals, Juncker said, adding that the operation would cost as much as 300 million euros (338 million dollars) over the next six months.
To comply with international law, people arriving from Turkey will retain the right to have their asylum claims heard in Greece before being sent back. The EU has pledged to cover the cost of the return operations.
The bloc has also promised Turkey a quicker disbursement of 3 billion euros (3.4 billion dollars) in already-promised refugee aid, as well as more financial support on top of that, to help it cope with more than 2 million Syrians it has taken in.
The United States called the agreement "an important step" on responding to the refugee crisis and commended Turkey for hosting more than 2.7 million refugees from Syria.
State Department spokesman John Kirby said the US strongly endorsed the action to shut down the illegal smuggling operations, adding that the US "stands ready to increase our support to affected countries and to help other nations neighboring Syria."
Contentious issues at the two-day EU summit in Brussels included Turkish demands for visa-free access to the bloc for its citizens by June - a step that will be granted so long as Ankara meets the required benchmarks in time.
EU leaders also managed to broker a compromise to advance Turkey in its long-standing bid to join the EU - a move initially resisted by Cyprus, which is in the midst of delicate reunification talks with the island's Turkish-backed north.
"Today we have a balanced proposal that takes on board Cypriot concerns," EU President Donald Tusk said following the talks.
The EU pledged to open negotiations on financial and budgetary provisions with Turkey before July. Ankara had initially sought progress on five negotiation chapters - policy areas in which Turkey must align with EU standards - that Cyprus had blocked.