Mahmut Tat had sought asylum in Sweden in 2015 after being sentenced in Turkey for six years and 10 months for alleged links to the PKK. His final asylum application was denied last year by the Swedish Migration Agency.

Swedish Migration Minister Maria Malmer Stenergard did not reply to requests for comment but told SVT that the government had played no part in the decision.

"It is about a deportation case where an individual has had his asylum application rejected," she told SVT. "The government has no role in ruling on asylum applications."

Turkish state television TRT said Tat was sent to an Istanbul prison on Saturday. Swedish authorities were not immediately available for comment.

Sweden and Finland applied in May to join NATO in response to Russia's invasion of Ukraine, but ran into objections from Turkey, which accused the two countries of harbouring militants from the banned Kurdistan Workers' Party (PKK) and other groups.

Turkey said on Wednesday that Sweden and Finland had made progress towards NATO membership but that they still needed to do more to satisfy Ankara's demands on tackling militant groups.

Others wanted by Ankara are people with alleged links to Fethullah Gulen - a Turkish cleric who lives in the United States and is accused of orchestrating 2016's failed coup attempt against Erdogan.

Stockholm and Helsinki deny harbouring militants but have pledged to cooperate with Ankara to fully address its security concerns and also to lift arms embargoes.

NATO makes its decisions by consensus, meaning that both countries require the approval of all 30 countries. Only Turkey still stands opposed to the two countries' membership.

(Reporting by Ece Toksabay and Johan AhlanderEditing by Ros Russell)