German Chancellor Angela Merkel said Europe cannot allow Greece to fall into chaos, amid sharp divisions among members over the migrant crisis.
Austria and several Balkan countries have introduced restrictions stranding migrants in Greece.
Merkel said EU nations had not battled to keep Greece in the euro just to leave it “in the lurch”.
She also defended her decision to open German borders to migrants, despite a resulting slump in her popularity.
More than one million people arrived to claim asylum last year, sparking opposition within her governing coalition and a rise in far-right extremism.
