The European Union needs to come up with an alternative plan for tackling migration after Turkey threatened to back out of an accord to help stem the influx of migrants to Europe, Greece's migration minister told German daily Bild.

Turkish Foreign Minister Mevlut Cavusoglu said over the weekend that Ankara would back out of the agreement with the EU if the bloc did not deliver the promised visa-free travel for Turks in return.

The 28-nation EU is dependent on Ankara to enforce the deal which has sharply cut the number of refugees and migrants leaving Turkish shores for Greece. Grappling with a major financial crisis, Greece struggled to cope with the influx.

‘We are very concerned,’ Greek Migration Minister Yannis Mouzalas told mass-selling Bild. ‘We need, in any case, a Plan B.’

German Vice Chancellor Sigmar Gabriel said on Monday Europe would not be blackmailed by Turkey in talks on visa liberalisation, which have been hampered by a dispute over Turkish anti-terrorism legislation and a crackdown after an abortive coup on July 15.

Mouzalas also called for a fairer distribution of refugees in Europe, many of whom arrive from Syria, Iraq and Afghanistan and head for Germany and Sweden. But some countries, including Hungary and Slovakia, have objected to proposed EU quota system for resettling migrants across the bloc.

‘The refugees must be distributed right away to all EU countries - and not just to individual (states),’ he said.

More than 257,000 migrants and refugees entered Europe by sea from the start of this year to July 27, and at least 3,000 have died, the International Organization for Migration (IOM) said on Tuesday.

These figures represent a sharp increase from the same period in 2015, the IMO said.