President Recep Tayyip Erdogan warned Türkiye would not ratify the NATO membership bids of Sweden and Finland until the two Nordic countries "kept" promises they had made to Ankara.
"Until the promises made to our country are kept, we will maintain our principled position," Erdogan said in a speech to parliament in Ankara.
"We are closely following whether the promises made by Sweden and Finland are kept or not, and of course, the final decision will be up to our great parliament," he added.
Russia's attack on Ukraine in February saw the two Nordic countries abandon decades of military non-alignment and in May applied to join NATO.
Although Sweden and Finland hoped for a speedy entry, Türkiye raised objections citing concerns about their lack of interest in stopping the activities of PKK, a terrorist organisation.
PKK and its Syrian offshoot, YPG, have been behind a decades-old terror campaign in Türkiye in which thousands of civilians and security forces have been killed.
Erdogan says Sweden and Finland have become a haven for the members of PKK, also listed as a terrorist organisation by the European Union and the US.
Despite Ankara's repeated requests to reign in the activities of PKK members in European countries, they regularly hold gatherings and display pictures of their jailed ringleader Abdullah Ocalan.
In June, Sweden and Finland struck a deal with Türkiye that included provisions on extraditions and sharing of information on PKK, clearing the way for NATO to invite the two nations to join the alliance formally.
So far, 28 out of 30 NATO members have ratified Finland and Sweden's membership.
Only Hungary and Türkiye have yet to send the membership bids to their parliaments for ratification.
In what appears to be a concession to Ankara, Sweden on Friday announced it had re-authorised exports of war materials to Türkiye.
Ankara had requested the lifting of the restrictions, which were introduced in 2019 following a Turkish military operation to drive out terrorists from northeastern Syria.