The Turkish minister for European Union affairs says he is losing hope of getting a deal on visa-free travel for Turks within Europe.

Last month's EU-Turkey deal on tackling the migrant flow has begun to produce results, a top EU official says.

Greek authorities are gearing up to send hundreds of failed asylum-seekers back to Turkey, which is racing to set up reception centres under a controversial EU deal.

There is growing concern over a lack of preparation for the plan to send migrants back from Greece to Turkey, two days before it goes into effect.