Updated

Denmark has summoned Turkey's ambassador over the disappearance of a man suspected of attempted murder who was arrested in Istanbul at Denmark's request.

Foreign Minister Martin Lidegaard says he will tell Mehmet Donmez on Friday that "it is clearly not satisfactory" that Turkey has not informed Danes why and when Danish national Basil Hassan was freed.

Lidegaard said Thursday the 27-year-old's release was "a huge problem."

Hassan, suspected in the failed shooting of a Danish anti-Islamist in 2013, was arrested April 16. On Wednesday, Turkey said that a Turkish court was behind his release without giving further details.

Some speculate Hassan could have been part of a Turkish government prisoner swap with the jihadi Islamic State group to secure the return of 49 captured Turkish diplomats.