The visit comes amid questions over the legality of the EU-Turkey pact, which deports back to Turkey migrants who do not qualify for asylum in Greece.

Human rights groups say Turkey is not a safe place to return people.

Turkish officials have warned the deal could collapse if demands for visa-free EU travel for its citizens are not met.

The agreement says Turkey must meet 72 conditions by 4 May to earn the visa waiver, but diplomats say only half of those points have been met so far.

Mrs Merkel is expected to visit a refugee camp in the southern city of Gaziantep, near the Syrian border, where she will meet Turkey`s Prime Minister, Ahmet Davutoglu.

She will travel with the European Council President, Donald Tusk, and the EU Commission Vice-President, Frans Timmermans.

Mrs Merkel has faced opposition in Germany for her migration policies and has defended the deal with Turkey despite opposition from some European partners.
Her trip comes as she faces additional pressure for agreeing to the prosecution of a German comedian accused of insulting Turkish President Recep Tayyip Erdogan.

Advocates of freedom of speech in both Turkey and Germany have called on Mrs Merkel to send out a strong message on the issue during her visit.

It has been over a month now since the migrant deal between the EU and Turkey was struck, but not everyone is convinced that it is working smoothly.

Although the number of migrants reaching Greece from Turkey has dropped by around 80%, few of staff promised by the EU to help enforce the deal have arrived, and many EU nations are dragging their feet to accept more migrants.

Angela Merkel said the aim of the visit was to see the living conditions of migrants in Turkey.

But more will be on the table, such as the promise of visa-free travel for Turkish citizens willing to go to Europe, which seems to be one of the most contentious issues.

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