Sweden's ruling Social Democrat party, which has until now rejected membership of NATO, is reviewing its international security policy in the light of Russia's invasion of Ukraine, it said on Monday.
The Social Democrats, the biggest party in parliament and who form a single party, minority government, have consistently rejected calls to join NATO, arguing that military non-alignment has served the country well.
But an increasingly belligerent Russia has forced a rethink across the political spectrum in both Sweden and neighbour Finland, which is also outside the 30-member NATO alliance.
"When Russia invaded Ukraine, Sweden's security position changed fundamentally," the Social Democrats said in a statement.
Daily DN quoted Social Democrat party secretary Tobias Baudin saying the review would be complete before the summer.
Finland is expected to outline its path regarding NATO in the coming weeks.
The Social Democrats reaffirmed their policy of military non-alliance in November last year and their stance is widely seen as the biggest hurdle to an application for NATO membership.
"The Social Democrats are the key (to membership)," Peter Esaiasson, political science professor at Gothenberg University, said.
Four centre-right opposition parties back a NATO application, with the leader of a fifth saying he wanted his party to support joining if Finland goes ahead as well.
The Left and Green Parties are against membership.
The Social Democrats said the review was more than a discussion about whether or not to join NATO and aimed to give members the opportunity to give their views on all aspects of security policy.
Prime Minister Magdalena Andersson and party leadership could still decide to apply to join NATO without the backing of the membership "if the need for a different security policy arises during the (review) process," the Social Democrats said.
(Reporting by Simon Johnson, Editing by Angus MacSwan)
