Nato Secretary-General Jens Stoltenberg has said that Finland and Sweden would be welcomed with open arms into the military alliance and could become members quite quickly.
His comments come amid a surge in support for joining the alliance in states close to Russia’s border following the invasion of Ukraine.
“It’s their decision,” Mr Stoltenberg said on Thursday. “But if they decide to apply, Finland and Sweden will be warmly welcomed, and I expect that process to go quickly.”
While he declined to give a time frame, Mr Stoltenberg suggested that both countries could be offered a form of protection from the time their membership applications are made to when they formally join.
He said he is “confident that there are ways to bridge that interim period in a way which is good enough and works for both Finland and Sweden”.
Nato’s Article 5 ensures the alliance must take collective military action if one state is invaded.
The prospect of Finland and Sweden joining Nato would enrage Russian President Vladimir Putin, who has asked the alliance to withdraw all of its troops from Russia’s borders.
The Kremlin has also demanded a formal guarantee that Ukraine will never join the alliance. As Ukraine is not a member of Nato, the alliance has not engaged in direct military confrontation with Russia.
Finland has been involved in dozens of wars against its eastern neighbour, including two fought with the Soviet Union from 1939-40 and 1941-44. Sweden has eschewed military alliances for more than 200 years.
Both countries put an end to traditional neutrality by joining the European Union in 1995 and deepening cooperation with Nato.
Stockholm is conducting a review of security policy, which could include a position on possible Nato membership, with the results due by mid-May.
Finland has said it is planning to decide on whether to apply to join the alliance “within weeks”.
Earlier this month, Finland’s Prime Minister Sanna Marin said her country had to be “prepared for all kinds of actions from Russia” and that “everything had changed” when Mr Putin decided to invade Ukraine.
Russia’s invasion of Ukraine has prompted a surge of pro-Nato sentiment in Baltic countries, with 68 per cent of Finnish respondents saying they were in favour of joining the alliance in a recent poll – more than double the figure before the war.