Turkiye has always supported the idea of expanding NATO, but it has concerns with regard to Finland and Sweden's desire to join the alliance given their relations with terror groups, the Turkish foreign minister said on Sunday.

Mevlut Cavusoglu's statements came after an informal NATO gathering held in Germany's capital Berlin.

"Countries supporting terrorism should not be allies in NATO," Cavusoglu said, adding that he briefed participating officials on the support the two countries provided to the PKK terror group, especially the arms aid supplied by Sweden.

Both Finland and Sweden "must stop supporting terror groups," and give clear security guarantees in order to become NATO members, said Cavusoglu, who noted that the member countries should show solidarity with one another.

Turkiye has made it clear why it opposes Finnish and Swedish membership for the time being and has expressed its discomfort related to the two countries' talks with members of the PKK and its Syrian offshoot, the YPG, Cavusoglu said.

He added that though many members of the alliance welcome the idea of Finland and Sweden joining the alliance, they also agreed that the Turkish concerns should be resolved.

Restrictions on export permits by the would-be NATO members are "unacceptable," he added, asserting that such constraints are adopted against hostile countries.

The minister went on to say that Turkiye's demands that the countries lift restrictions on its defense industry and exports should be regarded as an indication of the spirit of alliance, rather than a bargaining chip, because Ankara has concerns about the two countries.

During their three-way meetings, the Finnish and Swedish sides came up with proposals to address Turkiye's concerns, he said, underlining that identifying the PKK as a terror group alone would not meet the expectations of the Turkish government, which wants to see more tangible efforts.

Furthermore, Cavusoglu commented on his Swedish counterpart Ann Linde's statements on relations with terror groups, saying they were not "productive," but "provocative."

On the other hand, the Turkish top diplomat said his Finnish counterpart, Pekka Haavisto, has so far been cautious.

In its more than 35-year terror campaign against Turkiye, the PKK -- listed as a terrorist organization by Turkiye, the US, and the EU -- has been responsible for the deaths of over 40,000 people, including women, children and infants. The YPG is the PKK's Syrian offshoot.

For decades, Sweden and Finland adopted a neutral posture in the region in terms of their foreign policy, however, the war between Ukraine and Russia triggered a shift in their approach as they demonstrated their intention to join the NATO alliance.

At least 3,573 people have been killed and 3,816 injured since Russia launched the war on Ukraine on Feb. 24, according to UN estimates. The true toll is feared to be much higher.

Over 6.1 million people have fled to other countries, with some 7.7 million people internally displaced, according to the UN refugee agency.