With migrant numbers stacking up in Greece, there’s tough talk from Prime Minister Alexis Tsipras.

What we refuse to do is accept the transformation of our country into a permanent warehouse of souls and, at the same time, continue to act within the European Union and at summits as if there's nothing wrong

He says Athens will block future European Union agreements, if member states don’t do more to share the burden of the crisis.

Migrants are now getting trapped in Greece because of tougher border checks elsewhere.

Tsipras has made his position clear in the parliament.

“Some nations do not seem to comprehend that agreements, our common agreements, are either implemented, or there are no agreements,” said Tsipras.

“What we refuse to do is accept the transformation of our country into a permanent warehouse of souls and, at the same time, continue to act within the European Union and at summits as if there’s nothing wrong.”

Alexis Tsipras has threatened to veto a UK agreement unless states promise not to close their borders to refugees. pic.twitter.com/c0sG6X2Td4 — UK News (@UK__News) February 19, 2016

Tsipras has been meeting the top UN official for refugees, who is deploring the closing of borders.

Filippo Grandi has been on a fact-finding visit to Greece.

“We disagree with these measures and call once again for cooperation,” Grandi told Tsipras.

“The problem is we have called for cooperation for a long time now and we don’t get a response. So we need to find a convincing way to do it.”

Meanwhile, Austria has been hosting a meeting with Balkan states on the main migrant route into Europe.

It has brushed aside criticism from the EU, after setting off a so-called “domino effect” of frontier controls.

Those measures, from Austria’s border with Slovenia to the Former Yugoslav Republic of Macedonia’s border with Greece, are causing migrants to become stranded.

Vienna says it needs to coordinate national border controls, in the absence of European measures.