In a joint press conference held with Ulf Kristersson, leader of the opposition Moderate Party, Prime Minister Magdalena Andersson said joining the alliance would act as a deterrent against Russian aggression. 

“The government has decided to inform Nato that Sweden wants to become a member of the alliance,” Andersson told reporters a day after neighbouring Finland made a similar announcement.

“We are leaving one era and beginning another,” she said, adding that Sweden’s Nato ambassador would “shortly” inform Nato.

Ulf Kristersson, whose party has long supported membership of the alliance, said that he wanted to put party political differences aside to support the government in its decision.  

“There are many major issues where we think differently, but we are going to take a joint responsibility for the process of taking Sweden into Nato,” he said. 

Sweden and Finland have both expressed a desire to act in lockstep on Nato membership and submit their applications jointly.

“We expect it shouldn’t take more than a year” for the alliance’s 30 members to unanimously ratify Sweden’s membership application, Andersson said.

The announcement was expected after her Social Democratic party on Sunday backed membership, in a dramatic turnaround after having opposed the idea since the birth of the Western military alliance.

It came after a debate in parliament in which all parties apart from the Green Party and Left Party spoke in favour of Sweden joining the alliance.  

“It is now clear that there is a broad majority in Sweden’s parliament for Sweden joining Nato,” she said. 

After Sweden’s announcement, Denmark, Norway and Iceland published a joint statement in which they promised to Sweden “by all means necessary” if the country is attacked in the gap between application and admission to the alliance. 

“Should Finland or Sweden be victims of aggression on their territory before obtaining Nato membership, we will assist Finland and Sweden by all means necessary,” the three countries said. “We immediately initiate preparations in order to effectuate these security assurances.”

Russia’s president, Vladimir Putin, said on Monday that Sweden and Finland joining Nato did not represent a direct threat to Russia’s interests, but he said that if Nato began to site equipment on their territories, Russia would have to respond. 

“Russia has no problems with these states (Finland, Sweden). There is no immediate threat to Russia,” he said at a meeting of the Collective Security Treaty Organisation, which groups Russia with Belarus, Armenia, Kazakhstan, Kyrgyzstan and Tajikistan.

“But the expansion of military infrastructure into this territory would certainly provoke our response,” he said.  

Sweden’s defence minister Peter Hultqvist is flying to Washington on Monday, where he will meet his counterpart Lloyd Austin.