On Thursday, Sweden's top court blocked the extradition of two Turks that Turkey says are part of a terrorist group, potentially complicating Stockholm's bid to join NATO.

The move comes just days after Turkish President Tayyip Erdogan unexpectedly agreed to put Sweden's NATO bid to the country's parliament after months of delays.

Turkey is seeking the extradition of two Turkish citizens from Sweden on accusations they are part of the Gulen movement, which it designates a terrorist organisation.

However, Sweden's Supreme Court said there were legal obstacles to agreeing to Turkey's request in this case. The court said in a statement that in Turkey's view, the two committed a criminal act by joining the Gulen movement via a mobile application used by its members, but these actions alone did not equate to participation in a terrorist organisation under Swedish law.

Another obstacle is that the two people were at risk of persecution in Turkey, it said. A spokesperson for the Swedish Prime Minister declined to comment and a Justice Minister spokesperson did not reply to a request for comment.

A spokesperson for the Turkish Foreign Ministry was not immediately available. In an interview published by Turkish media on Thursday, Erdogan said he expects European Union countries to take some steps on updating a customs union and visa-free travel, and NATO countries to lift restrictions on arms sales to Turkey.

He also said he will forward the NATO application to parliament when it reopens in October, but that Ankara still needs to see some concrete steps against terrorism from Stockholm, with extraditions a priority.

"The concrete steps in relation to the promises that were made primarily include ending the activities of terrorist organisations in the countries in question, (and) the repatriation of the terrorists," he was quoted as saying. "From now on, we will act according to whether the promises that are made are implemented."