Turkey must back off from its refusal to change its anti-terror laws if it hopes to secure visa-free travel to Europe for Turkish citizens, according to top European Union and German officials.

The visa waiver is one of the incentives offered by the EU for Turkey to stop migrants leaving for Europe and take back those who do arrive.

Turkey has to fulfil 72 conditions to secure the visa waiver, and has fulfilled most of them.

However, statements in recent days by President Recep Tayyip Erdogan and others that Ankara will not narrow its definition of "terrorist" and "terrorist act" have raised concerns that journalists and political dissenters could be targeted.

Mr Erdogan has warned that the entire migrant deal could collapse if the Europeans renege on their pledges.

Prime Minister Ahmet Davutoglu, a key negotiator of the deal, announced last week that he will step down later this month.

German foreign minister Frank-Walter Steinmeier acknowledged that "we have a strong interest in this agreement on migration not collapsing".

However, he said he cannot influence Ankara's stance on the anti-terror law and "the ball is in Turkey's court".

He said that "if Turkey fulfils its commitments", the EU should too.

The head of the European Commission, also speaking at a forum on European policy in Berlin, said Brussels is counting on Turkey sticking to the conditions - including the changes to anti-terror laws.

"That's how we agreed it with Turkey, and the consequence of the change in the office of the Turkish prime minister cannot be that agreements between the European Union and Turkey are disavowed," Jean-Claude Juncker said.

"We put the greatest value on the conditions being fulfilled, otherwise this deal... will not happen.

"If Mr Erdogan is pursuing the strategy of denying Turks the right to free travel to Europe, then he will have to take responsibility for that to the Turkish people.

"That isn't my problem. It will be his problem."