Turkey on Friday threatened to block NATO's enlargement process with the two Nordic countries, which requires the unanimous approval of the alliance's members.

"The Swedish foreign minister's statements are unfortunately not constructive. She continues to make provocative remarks," Cavusoglu told reporters in Berlin on the sidelines of an informal meeting of NATO foreign ministers.

The minister struck a more conciliatory tone towards Finland, which he described as "very respectful" in the face of Ankara's "concerns".

"But we don't see the same thing in Sweden," he insisted.

Turkish President Recep Tayyip Erdogan on Friday criticised the two countries for serving as "safe havens for terrorists of the PKK", the Kurdistan Workers' Party, which is blacklisted as a terrorist organisation by Turkey, the European Union and the United States.

"We have always supported NATO's open door policy," Cavusoglu said.

"But the fact that these two countries are in contact with members of a terrorist organisation, that Sweden sends them weapons and that they impose restrictions on the export of defence equipment to Turkey goes against the spirit of alliance."

Cavusoglu said he was waiting to see what guarantees would be offered by the two countries.

"It is absolutely necessary to end support for terrorist organisations and lift restrictions on exports to Turkey. I'm not saying that as a bargaining chip, but because that's what it means to be allies," he said.

NATO Secretary General Jens Stoltenberg voiced confidence Sunday at resolving Turkey's concerns and stressed that Ankara was not seeking to block the two countries' membership.

"I am confident we'll be able to find common ground, consensus on how to move on membership issues," Stoltenberg told reporters virtually at a NATO meeting in Berlin.

Several NATO member states said Sunday they were "on the right track" to reach a consensus on the integration of Finland and Sweden, with Berlin even saying their membership could come "very quickly".