Ankara, June 16 : Turkish President Recep Tayyip Erdogan and NATO Secretary General Jens Stoltenberg held a discussion over the membership bid of Sweden and Finland to the military alliance. During their phone call on Wednesday, Erdogan reiterated his stance that steps should be taken to address Turkey's "legitimate concerns" about Sweden and Finland's NATO membership requests, Xinhua news agency quoted an official statement issued in Ankara as saying. Erdogan told Stoltenberg that Turkey wants written assurances from the two Nordic countries in order to make progress in their NATO membership. He emphasised that they "cannot achieve progress in the process without concrete steps that meet Turkey's rightful expectations, and without giving written commitments to a paradigm shift in the fight against terrorism and defence industry cooperation", the statement said. Sweden and Finland formally applied to join NATO in May following the Russia-Ukraine war that erupted in February. NATO allies, except for Turkey, have welcomed the two countries' proposals. Accession of new member states requires consensus among existing NATO members. Ankara, however, citing the Swedish and Finnish ties with the Kurdistan Workers' Party (PKK) and other anti-Turkey groups, objected to their entry into the alliance. The PKK, listed as a terrorist organisation by Turkey, has been rebelling against the Ankara government for more than three decades. Turkey also accuses the two countries of harbouring members of the Gulen Movement, which Ankara says is behind the failed military coup attempt in 2016. /IANS