South-eastern Europe’s “Balkan route”, the main passage for migrants to reach more affluent countries to the north, will remain closed permanently, Austria’s Interior Minister Johanna Mikl-Leitner told German newspaper “Die Welt” on Thursday.

On Wednesday, Macedonia sealed its border with Greece to illegal migrants after Slovenia, Croatia and Serbia, which are on the way to Austria, announced tight new restrictions on migrant entry.

“My position is clear: the Balkan route remains closed and that permanently,” Mikl-Leitner told the newspaper.

She said only such a “consistent signal” will deter migrants, many of them fleeing war and conflict in the Middle East and beyond, from crossing the Mediterranean from Turkey to reach European shores.

As a result of the route’s closure, thousands of migrants have built up on the Greek side of the Macedonian border and around 1,000 more are stranded in a refugee camp on the Macedonian side of the Serbian border.

“This alliance of reason has so far provided the decisive contribution to preserve stability and order for the people in Europe,” Mikl-Leitner said in reference to the Balkan countries along the route.

In late February, Austria set off what it called a “domino effect” of national restrictions by imposing daily caps on the number of migrants to limit the flow of people toward it.

Last year, over 1.5 million migrants arrived in Europe, unleashing fierce political debates across the continent over how to handle the crisis.