German Chancellor Angela Merkel has blamed European nations for “unilaterally” shutting the Balkan route for migrants.
She said this had put Greece in a “very difficult situation” and such decisions should be taken by the whole of the EU.
Austria, Slovenia, Croatia, and non-EU members Serbia and Macedonia have all acted to stem the migrant flow.
The EU and Turkey, from where migrants reach Greece, have set out a plan to ease the crisis.
Under the proposals, hammered out at a summit in Brussels on Monday but still to be finalised, all migrants arriving in Greece from Turkey would be sent back. For each Syrian returned, a Syrian in Turkey would be resettled in the EU.
European Council President Donald Tusk has said the plan would spell the end of “irregular migration to Europe”.
It is the worst such crisis in Europe since World War Two.
The move to close the Balkan route began with Austria announcing it would limit the number of migrants crossing its border.
Then, late on Tuesday, Slovenia said it would allow in only migrants who planned to seek asylum in the country, or those with clear humanitarian needs.
