Vienna (AFP) - German Chancellor Angela Merkel, under fire at home over her refugees policy, called Saturday for Europe to secure deals with third countries to send back migrants who do not qualify for asylum.

Speaking after talks in Vienna with leaders along the Balkan migrants trail into Europe, Merkel said the continent must "stop illegal immigration while living up to our humanitarian responsibilities".

To this end "it is necessary to get agreements with third countries, especially in Africa but also Pakistan and Afghanistan... so that it becomes clear that those with no right to stay in Europe can go back to their home countries," she told reporters.

Last year hundreds of thousands of people, many fleeing the Syrian war, trekked up from Greece through the western Balkans to northern Europe, in the continent's biggest migration crisis since 1945.

Populist parties across Europe have stoked concerns about the influx, not least Alternative for Germany (AfD), which has stolen support from Merkel's centre-right party in recent state elections.

On Monday Merkel said for the first time that the influx could have been better handled.

In March, under pressure from Austria, Balkan countries closed their borders, and the flow has since slowed dramatically, although 100-150 still make it to Austria every day, Vienna says.

The same month the EU struck a deal with Turkey -- home to more than three million refugees -- under which Ankara promised to halt the inflow in return for billions in aid and other sweeteners.

The pact may yet collapse, however, in the wake of the July 15 coup attempt in Turkey.

- Greece under strain -

As illustrated by a large fire at a refugee camp on the island of Lesbos on Monday, Greece meanwhile remains under severe strain, with more than 60,000 people stranded.

An EU scheme to relocate them -- and others in Italy -- around the bloc has failed to live up to expectations, while extra administrative assistance promised by the EU has been insufficient.

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Merkel on Saturday said that EU countries' participation in the relocation scheme has been "too slow", saying this could "increase the pressure" on Greece's border with Bulgaria.

"It is unacceptable that the countries that first receive (the migrants) bear the burden," Greek Prime Minister Alexis Tsipras said in Vienna, according to ANA.

"This is also a question that concerns destination countries."

Bulgaria, the EU's poorest country, is home to around 10,000 stranded migrants although Brussels has promised Sofia extra support including help from a new EU border force from October 6.

- 'Closed for good' -

EU President Donald Tusk, also in Vienna, said that it was necessary "to confirm, politically and in practice, that the western Balkan route of irregular migration is closed for good".

The difficulties of making it through to the Balkans is thought to be prompting increasing numbers to attempt treacherous sea crossings from Libya or Egypt to Italy instead.

More than 300,000 migrants have crossed the Mediterranean this year, the UN said on Tuesday. Some 3,500 have perished in the attempt. On Friday more than 160 drowned off Egypt.

Echoing Merkel, Hungarian Prime Minister Viktor Orban said Saturday that this showed that the EU needed to send people back to Egypt, Libya and other countries.

Orban, who has been scathing about Merkel's "open-door" policy and has called immigration "poison", has refused to take in a single migrant under the EU relocation scheme.