Sweden’s top court ruled today that there are legal obstacles to the extradition of two Turks who Ankara says are members of a terrorist organization, possibly complicating Stockholm’s bid to join NATO days after Turkey lifted its objections to Sweden’s admission.

Turkish President Tayyip Erdogan agreed on Monday to advance Sweden’s bid to join NATO in the Turkish parliament after months of delays. Ankara accuses Stockholm of doing too little to deal with people Turkey considers terrorists, with their extradition a “thorn in the side”.

Turkey is currently seeking the extradition of two Turkish citizens from Sweden on charges that they belong to the Gulen movement, which has been designated a terrorist organization. Turkey claims US-based preacher Fethullah Gulen is behind the 2016 coup attempt.

The Swedish government decides on extradition requests and has the final say. But the country’s Supreme Court said there were legal obstacles to agreeing to Turkey’s request.

“The criminal acts (in Turkey’s view) consisted of persons joining the Gülen movement by downloading and using a mobile application used by members of the movement,” the court said in a statement.

Those actions alone do not amount to membership of a terrorist organization under Swedish law, the court said, adding that extradition must be based on actions that constitute a crime in Sweden and Turkey.

Another obstacle is that these two persons are at risk of prosecution in Turkey, according to the court.