By Friederike Heine

Berlin (dpa) - Chancellor Angela Merkel said Wednesday that this week's EU summit will decide whether the bloc's deal with Turkey to stem the refugee influx should be pursued or abandoned in favour of a barrier along Greece's borders with Bulgaria and Macedonia.

Merkel told the German parliament that the two-day summit starting Thursday would determine whether the current measures to fight the root causes of migration and to jointly secure the EU's external borders would be enough to bring the refugee crisis under control.

The alternative would be to "abandon [this path] and close the Greek-Macedonian-Bulgarian border instead - with all the consequences that would entail for Greece and the European Union as a whole."

The chancellor was referring to a suggestion from four Central European countries - Poland, Hungary, Czech Republic and Slovakia - that say Europe needs an alternative plan if the current measures fail.

Their so-called "Plan B," which Austrian Chancellor Walter Faymann also advocates, calls for a barrier along Greece's borders with Bulgaria and Macedonia, which EU officials have warned would effectively exclude Greece from the visa-free Schengen zone.

Only after a decision is made on the implementation of an EU-wide scheme to internally redistribute 160,000 asylum seekers could EU leaders start talking about a permanent resdistribution mechanism, Merkel said.

The chancellor's decision to keep German borders open and work to solve the refugee crisis with EU partners has received strong criticism at home and within the ranks of her own conservative alliance.

However, European Commission President Jean-Claude Juncker gave his firm backing to Merkel in an interview with mass circulation newspaper Bild on Wednesday, saying that she would "outlast all her critics in office."

"The European migration policies [Merkel] and I are pursuing will prevail," Juncker said. "It is political leadership to say 'we can do it.' Anything else is capitulation to the populists."

Juncker also pointed to progress that has already resulted from the Turkey deal. The number of people entering Greece from Turkey has fallen, and nine out of 10 migrants are now being fingerprinted on arrival, he said.

But Austria's Faymann said that, though he supported Merkel's coordinated EU push, it would not be enough to control migration and that border controls at the national level were necessary.

"We have taken steps that Germany will also take [in due course]," he told Austrian newspaper Kurier, referring to his government's decision to impose daily quotas on refugee arrivals. "I am convinced that we will be in sync again soon."

German Justice Minister Heiko Maas said Wednesday that the survival of Schengen rested on the ability to secure the EU's external borders, and lent his support to Merkel's effort to resist unilateral measures.

"Our ideals of peace, freedom and justice are only possible if we act in unison as Europeans," he said.

Later Wednesday, Juncker and EU President Donald Tusk are to hold talks with the leaders of Croatia, Slovenia, Serbia and Macedonia to discuss cooperation along the Western Balkan route.