Kim Hjelmgaard

USA TODAY

MUNICH — The European Union warned Greece on Friday to do a better job of stemming the flood of migrants crossing through to other European nations or face a suspension of the EU's passport-free travel rights.

The ultimatum — fix Greece's border controls within three months or lose free travel rights for up to two years — came as the 28-nation bloc struggles to cope with its worst refugee crisis since World War II.

Greece is the main gateway for several thousand migrants a day who are fleeing wars in Syria and elsewhere en route to more prosperous northern Europe. EU leaders have accused Greece of not doing enough to keep so many war refugees and other migrants seeking better economic opportunities from transiting through the country.

"The overall functioning of the Schengen Area is at serious risk," the European Council said, referring to a 28-nation European zone that allows for passport-free travel for more than 400 million citizens, business people, tourists and others. "The difficulties faced by Greece have an impact on the EU as a whole."

Schengen Area countries are permitted to unilaterally put up border controls for a maximum of six months, but that time limit can be extended for up to two years if a member is found to be failing to protect its borders.

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France and Austria have imposed temporary border controls, and European Council President Donald Tusk has warned that the free-travel zone faces collapse if migration to Europe is not brought under control.

The European Council gave Greece a list of changes it wants met, including overhauling its "registration procedures, sea border surveillance, border check procedures, risk analyses, human resources and training, infrastructure and equipment and international cooperation."

The International Organization for Migration, a group that tracks people fleeing conflict zones, said Friday that an estimated 83,201 migrants arrived in Europe so far this year, 77,303 of them arriving on Greek islands from Turkey. More than 850,000 migrants arrived in Greece last year.

Greece, which has been coping with an enormous debt burden that required a massive international bailout last year, has complained that it lacks financial resources to manage such a huge flow of people.

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NATO said this week that it would start patrolling the Aegean Sea as it steps up efforts to clamp down on smugglers who are ferrying migrants across the Mediterranean Sea to Europe .

The development came as the 52nd Munich Security Conference kicked off Friday in this Bavarian capital. World leaders and diplomats held talks on subjects ranging from cyber-security to the Islamic State terror group to the migrant crisis.

Wolfgang Ischinger, chairman of the conference, said in his welcoming remarks that the world is at a more dangerous point than at any time since the Cold War.

Jordan's King Abdullah whose country is hosting more than 600,000 Syrian refugees, cautioned that the EU needed to do more to help nations on its doorstep with large Muslim populations, such as Kosovo and Albania, to halt the spread of radical Islam.

And speaking about how long the crisis may go on for, Italian Foreign Minister Paolo Gentiloni said "sorry to say this, but we are dealing with something permanent."

In Berlin, actor George Clooney and his wife Amal, a human rights lawyer, met with German Chancellor Angela Merkel to discuss the crisis. He is in Germany to attend the Berlin International Film Festival.

Clooney told reporters Thursday that he "absolutely agreed" with Merkel's decision to welcome more than 1 million migrants to Germany last year, a move that won international plaudits but has provoked an anti-immigrant backlash at home.