European Commission President Jean-Claude Juncker voiced concern today about the future of Europe's open border system in a call with German Chancellor Angela Merkel, after a report that Berlin might reimpose frontier controls temporarily.

"I just spoke with Chancellor Merkel. We agree: to keep borders open between EU-MS (member states), we need more Europe and solidarity in managing refugee crisis," the EU chief executive tweeted, referring to his efforts, in conjunction with Germany, to promote an EU-wide distribution of asylum-seekers.

A short time earlier, Juncker's chief-of-staff Martin Selmayr tweeted: "Free movement (Schengen) will be in danger if EU Member States don't work together swiftly and with solidarity on managing the refugee crisis."

In a series of tweets during the day, Juncker has recounted calls to east European leaders opposed to his proposals to share out asylum-seekers, including the leaders of Hungary, Slovakia and the Czech Republic. EU interior ministers meet in Brussels tomorrow to consider measures Juncker put forward last week.

German warnings to its eastern neighbours that their own citizens' much valued freedom to travel westward across the open borders of the Schengen passport-free area was under threat from the chaotic movements of refugees this summer have been part of a strategy to secure support for the EU executive's plans.