NATO membership for Sweden and Finland is a “top priority”, according to its secretary general, Jens Stoltenberg.
Both Scandinavian countries are to join the military alliance but their admissions have been stalled by two countries out of the 30 members – Turkey and Hungary.
Turkey had agreed to drop a block on the Nordic countries in June last year.
However, protests stalled talks between Ankara and Sweden after a far-right activist burnt a Koran in front of the Turkish embassy in Stockholm in January.
Despite this setback, Mr Stoltenberg said Turkey agreed to resume talks with Finland and Sweden on their membership bids in Brussels early next month and iron out any issues.
Speaking at a news conference with Finnish Prime Minister Sanna Marin, the Nato chief said: “I am absolutely confident that both Finland and Sweden will become members of NATO.”
Mr Stoltenberg, of NATO member country Norway, added that the Hungarian Parliament “made it clear” that it would deliberate ratification in a few days and he hoped for a positive imminent vote.
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He said: “My message has been for a long time… that time has come to finalise the ratification process. The time is now to ratify in both Budapest and in Ankara.”
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He reiterated that both Scandinavian nations fully meet Nato’s entry criteria and “have delivered on what they were supposed to do” after they applied to join the alliance in May.
Ms Marin hinted that the slow accession process for the two countries risked eroding NATO’s credibility and its open-door policy for new members.
NATO requires unanimous approval from its existing members to admit new ones into the alliance.
Finland’s parliament is ready to approve legislation permitting the country to join the organisation.
