European Commission President Jean-Claude Juncker and Austrian Chancellor Werner Faymann warned Wednesday that fences were not welcome in the EU, after Vienna suggested it could build a barrier on its border with Slovenia to control an influx of migrants.

"The President and the Chancellor repeated their common position that fences have no place in Europe," the two men said in a statement after a telephone call on the latest developments in the refugee crisis.

Austria and Slovenia have become key transit points for tens of thousands of refugees and migrants seeking to reach northern Europe ahead of the winter.