A crackdown in Turkey on academics and activists accused of supporting anti-government protests in 2013 will be raised by top EU officials when they visit Ankara on Thursday.

The European Union's foreign policy chief, Federica Mogherini, and Neighbourhood Policy Commissioner Johannes Hahn are set to hold talks with Turkish Foreign Minister Mevlut Cavusoglu.

While the EU called last week's arrests "alarming," Turkish President Recep Tayyip Erdogan on Wednesday defended the action against people he said were intent on toppling the government.

Brussels and Ankara have a strained relationship. Turkey has been an EU membership candidate for almost 20 years but has regressed on the bloc's benchmarks in areas such as the rule of law, citizens' rights and media freedom since an attempted coup in 2016.

Earlier this month, Hahn joined those calling for the accession talks with Ankara to officially end - a decision that would be up to EU member states. The European Commission has stressed that it does not share his view.

Yet, Brussels is heavily reliant on Turkey to help tackle the issue of migration. A deal signed with Ankara in early 2016 stemmed the flow of migrants headed for the EU from the Middle East, helping to end the migrant crisis that hit the bloc in 2015.

Turkey hosts more than 3.5 million refugees from neighbouring Syria. Under the 2016 deal, the EU helps fund their basic needs, although Ankara has repeatedly accused Brussels of failing to deliver on its pledges.