NATO membership applicants Sweden and Finland must take concrete steps on tackling terrorism, Presidential Communications Director Fahrettin Altun said Tuesday.

Commenting on Sweden and Finland's NATO bids at a panel discussion in the capital Ankara titled "NATO In The 21st Century: Challenges, Partnerships and Enlargement," Altun said their admission could be a threat to the bloc's future unless they take "a clear position on the fight against terrorism."

It is out of the question for Turkey to approach membership bids of the countries positively unless they take a "sufficiently determined position on the terrorist organization," he said, referring to the PKK.

Sweden and Finland formally applied to join NATO last month – a decision spurred by Russia's war on Ukraine, which began on Feb. 24.

But Turkey, a longstanding member of the alliance, has voiced objections to the membership bids, criticizing the countries for tolerating and even supporting terrorist groups.

All membership applications must be met by unanimity in the 30-member alliance to be successful.

Ankara's main demands are for the Nordic countries to halt support for the PKK and the YPG terrorist groups present on their territory, and to lift their bans on sales of some arms to Turkey. Ankara says the arms ban against an ally is inappropriate for prospective members of the security pact.

NATO should focus on determining common enemies, Altun added, urging the security alliance to show the same sincerity to every member state's security concerns.

"Today's global threats are much more complex ... it is of great importance for NATO to be able to increase solidarity and cohesion by taking into account the security concerns of its member states," he said.

"The importance of the indivisibility of security within the alliance must be clearly understood, and in this direction, a joint fight against terrorism must be carried out."