Left-wing European leaders tried to forge a common front Saturday in the continent's migrant crisis while right-wing and extreme right groups protested current policies toward the waves of people fleeing war and poverty.

The meetings and demonstrations came as thousands of migrants have massed in muddy camps in the Greek border town of Idomeni after countries across the Balkans closed their borders.

Europe's migrant crisis is forming the backdrop for key elections in three German states Sunday. The Alternative for Germany party, or AfD, is expected to make gains amid unease over Chancellor Angela Merkel's welcome last year for large number of refugees. However, German Vice Chancellor Sigmar Gabriel said Saturday that gains for the nationalist party won't change his government's stance.

"There is a clear position that we stand by: humanity and solidarity. We will not change our position now," said Gabriel, speaking after a meeting with European leaders in Paris.

But in Berlin, about 2,000 right-wing demonstrators carrying German flags chanted "Merkel must go!" and "We are the people!" in a protest Saturday, accompanied by a heavy police escort.

Greek Prime Minister Alexis Tsipras said the meeting of left-wing politicians made progress on a common progressive front to tackle the migrant crisis and called the rise of extreme-right forces the "real threat" to Europe.

Earlier Saturday in northern France, extreme right-wing youths torched tires and blocked migrants from roads in the port of Calais, leading to several arrests. And in Sweden, police said two fires overnight damaged planned shelters for unaccompanied minor migrants.

European leaders face complex negotiations next week on a deal to send migrants back to Turkey. In exchange, European countries would take in Syrian war refugees currently in Turkey.

Some have criticized Germany, which has taken in the majority of the more than 1 million migrants who have entered Europe over the past year, for dominating the discussions.

French President Francois Hollande on Saturday urged more "clarification and transparency" in the discussions with Turkey.

Hollande also said "there must be protection of the external borders" of Europe to avoid the re-establishment of new internal borders in Europe's travel-free zone.

Austria's interior minister said her country is getting ready to reinforce controls at more border crossings if migrants seek new routes into Western Europe. Interior Minister Johanna Mikl-Leitner also told the Welt am Sonntag newspaper it would be wrong to assume that mass migration into Europe is already over.