Mahmut Tat, who was sentenced to six years and 10 months in jail for PKK membership in Turkey, fled to Sweden in 2015 but his asylum request was rejected.

Tat arrived in Istanbul on Friday night having been detained by Swedish police, the Anadolu news agency reported.

He was taken by Turkish police soon after arriving at Istanbul airport and referred to court on Saturday, the private NTV broadcaster reported.

Turkey has accused Finland and Sweden in particular of providing a safe haven for outlawed Kurdish groups it deems "terrorists", and held back on ratifying their NATO bids despite an agreement in Madrid in June.

Finland and Sweden dropped decades of military non-alignment and sought to join NATO in May, after Russia invaded Ukraine.

The decision requires a consensus within the US-led defence alliance, but only Turkey and Hungary are yet to ratify their membership.

Foreign Minister Mevlut Cavusoglu held trilateral talks with his Swedish and Finnish counterparts on the margins of a NATO meeting in Bucharest this week.

"The statements (coming out of Sweden) are good, the determination is good but we need to see concrete steps," Cavusoglu said.

Ankara has said it expects Stockholm to take action on issues including the extradition of criminals and freezing of terror assets.