European Commission chief Jean-Claude Juncker backed Angela Merkel's welcoming stance towards migrants on Friday ahead of a mini-summit of leaders this weekend aimed at tackling record arrivals.
Juncker's comments came as Slovenia warned it could build Europe's latest border fence to stem the world's biggest migration crisis since World War II, unless it gets more help from the summit.
Hostility towards migrants streaming into Europe is mounting, with Germany on Thursday foiling an extremist plot to torch migrant shelters and Swedish police saying a sword attack on a school with many immigrant pupils was motivated by racism.
Most of the migrants -- a stream of more than 670,000 coming into Europe this year, mainly fleeing violence in Syria, Iraq and Afghanistan -- want to get to Germany, the EU's economic powerhouse.
Merkel's open-door policy faces a backlash as Germany braces for up to a million asylum requests this year, but Juncker said that "I appreciate very much that the Chancellor does not change course because of opinion polls".
"It is not a question of short-term popularity but the very substance of what politics is about," Juncker, who is hosting Sunday's mini-summit on migration, was quoted as telling the Funke-Mediengruppe press group about Merkel.
- Growing hostility -
In a sign of the growing stress on Germany, police in the southern town of Bamberg arrested 13 members of a far-right movement suspected of planning arson attacks on two homes for asylum seekers, prosecutors said Thursday.
Sweden is the EU's other top destination for asylum seekers, and police there said a sword-wielding man who killed two people at a school in the southwestern town of Trollhattan was a "racially motivated" hate crime.
That conclusion was based on the 21-year-old assailant's "attire, his behaviour at the scene of the crimes". He was named in the media as Anton Lundin-Pettersson.
A country of 9.8 million, Sweden expects to receive up to 190,000 asylum applications this year.
Greece meanwhile saw a record 48,000 arrivals in the past week, most of them coming by sea from Turkey, according to the International Organisation for Migration.
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Slovenia has become the main entry point into the European Union's passport-free Schengen zone from the increasingly crowded Balkan route after Hungary sealed its southern borders with razor-wire fences to stop migrants desperately trying to reach northern Europe before winter sets in.
With thousands more people arriving from Croatia on Friday, Slovenian Prime Minister Miro Cerar said he hoped Sunday's EU meeting would bring solutions but did not rule out a barrier along the 670-kilometre (415-mile) frontier with Croatia.
"We are considering that option too but at this moment... we are still looking for a European option," Cerar told state TV late Thursday.
Ljubljana has asked Brussels for 140 million euros ($155 million, £100 million), in addition to police backup and logistical support.
"If on Sunday we do not get sufficient (grounds for hope), if we see there is no will for collaboration, then all possibilities will are available, seeing as we will have been left alone," Cerar said.
More than 47,500 people have entered the small Alpine nation, which has a population of just two million, since October 17 when Budapest shut its frontier with Croatia, barely a month after also closing its Serbian border.
- Mini-summit -
Meanwhile the foreign minister of neighbouring Austria, Sebastian Kurz, warned the "surge into Europe" had become too big, as some 14,000 people were waiting in Slovenia on Friday morning hoping to continue to overstretched Austria.
The worrying new figures raised the pressure ahead of Sunday's meeting in Brussels grouping the leaders of Macedonia and Serbia along with the leaders of eight countries from the 28-nation EU: Austria, Bulgaria, Croatia, Germany, Greece, Hungary, Romania and Slovenia.
"The aim is to enhance cooperation, consultation and operational action in tackling the refugee crisis in particular in response to the emergency situation faced by the countries along the Western Balkans migratory route," Juncker's spokesman Margaritis Schinas told reporters.
"The past weeks have shown that there is no national solution to the problem... Only a European collective cross-border approach based on cooperation can succeed."
The European Commission meanwhile played down the slow start to a plan agreed by EU leaders in September to share out 160,000 refugees around the EU to take the pressure of frontline states Greece and Italy.
It said that so far only nine countries had formally offered to relocate 854 people but Schinas said it was an "evolving situation."