Hungary became the last NATO country still to give the legal green light to Swedish membership after the Turkish parliament ratified Stockholm's application on Tuesday and President Tayyip Erdogan signed off on the approval on Thursday.

All of NATO's 31 members have to ratify an applicant country's accession before it can join the alliance.

Stoltenberg, secretary general of the North Atlantic Treaty Organization, said Hungarian Prime Minister Viktor Orban had assured him in a telephone call this week and that he supports Sweden's accession.

"Swedish membership in NATO will make NATO stronger and all of us safer," Stoltenberg told reporters at NATO headquarters.

"It has been made clear that the parliament will take up this as soon as the parliament convenes and the message is that the parliament will then support ratification of Swedish membership," Stoltenberg said.

"The message I have received is that the parliament will reconvene at the end of February so we have to wait for that," he added.

"But I am absolutely confident and I count on Hungary that the ratification of Sweden will be ratified as soon as the parliament reconvenes at the end of February."

(Reporting by Bart H. Meijer and Andrew Gray; editing by Philip Blenkinsop)