Merkel: euro and open borders 'directly linked'

She added that if countries were to close their borders again, the single market would “suffer massively”.

Europe's open borders, as laid down in the 1985 Schengen agreement, pre-date the introduction of the single European currency in 2002.

All EU members are part of the single market. And while not all EU countries have the euro, all eurozone members in mainland Europe are part of Schengen.

But the lack of border controls has left Europe overwhelmed by an influx of refugees and migrants.

'Vulnerable'

“Now all of a sudden we are facing the challenge that refugees are coming to Europe and we are vulnerable, as we see, because we do not yet have the order, the control, that we would like to have,” noted the German leader, adding that the EU must strengthen its external borders to guarantee a passport-free internal territory.

Otherwise Europe would “reach an alternative which will certainly cost us a lot of energy”.

Meanwhile, Germany has increased the number of migrants it sends back to Austria. Many transit through Austria to reach Germany on their route from the Balkans, Greece and the Middle East.

Austria

“The daily number of migrants being turned back has risen from 60 in December to 200 since the start of the year,” said an Austrian police spokesperson according to AFP.

Those sent back were refugees from Afghanistan, Algeria, and Morocco, who wanted to pass through Germany and apply for asylum in Scandinavian countries, the agency reported Monday.

“German politicians seem to have decided to act with more firmness. The difficult thing [for us] is to explain if a migrants asks: Why can't I travel further now if my friend could still do it last week?”, added a second police spokeswoman from the state of Upper Austria.

While Austrian police said they received no explanation, and a German police spokesperson told Reuters “the valid legal rules (…) haven't changed”, there is one important variable that has changed since the new year started.

Merkel has come under political pressure to act after groups of men, many with a migrant background, assaulted women on New Year's Eve in Cologne and other cities.