Turkey's President Recep Tayyip Erdogan has warned that he will let hundreds of thousands of migrants travel on to Europe if pushed by the EU.He was reacting to a non-binding vote by the European Parliament to freeze talks on EU membership for Turkey.
The MEPs were alarmed by Mr Erdogan's "disproportionate" response to a failed coup attempt in July.
The migrant numbers reaching the Greek islands have dropped since an EU-Turkey deal in March to curb the influx.
President Erdogan accused the EU of breaking its promises. As part of the March deal, Turkey was promised aid, visa-free travel for its nationals and accelerated membership talks.
"Listen to me: these border gates will be opened if you go any further," he warned the EU on Friday.
A spokeswoman for German Chancellor Angela Merkel, Ulrike Demmer, said the deal was in the "interest of all parties" and that "threats on either side are not helpful".