The European Union should agree on criteria for accepting migrants and on how to secure the Greek border, where most of them arrive in Europe, Croatia's president said Thursday.

Kolinda Grabar-Kitarovic met with Poland's President Andrzej Duda and was was later to meet with Prime Minister Beata Szydlo.

With Duda she discussed the migrants crisis, the region's security in the face of a perceived threat from a resurgent Russia and closer economic and trade cooperation.

She later told reporters that the EU should set criteria for accepting refugees and economic migrants and should discuss ways of securing the border with Turkey, while taking a humanitarian approach to the crisis.

"We must work jointly and solve problems where they appear," Grabar-Kitarovic said.

Referring to a NATO summit that will be held in Warsaw in July she said she hopes the alliance will act quickly to accept Montenegro as a member, which would help strengthen security in the Balkans. Last year NATO invited Montenegro into accession talks.

Duda stressed that Poland would like the summit to take firm decisions on establishing a permanent presence of NATO troops in the region, where countries are concerned for their security because of their proximity to Russia.

On Wednesday, Grabar-Kitarovic and Duda attended ceremonies marking 71st anniversary of the liberation of the Nazi German death camp of Auschwitz, in southern Poland.