The survey by pollsters Sifo, published by the Svenska Dagbladet newspaper, suggests a sharp change in public opinion in the traditionally non-aligned Nordic country.
Of the 1,000 respondents, a total of 41 percent told the poll they were in favour of seeking membership in the military defence alliance, 39 percent said they were against it and 20 percent were uncertain.
“I'm surprised at how rapidly it has changed,” said Wilhelm Agrell, professor of intelligence analysis at Lund University, who published an opinion piece in the Dagens Nyheter on Sunday in which he argued Sweden should apply for Nato membership together with Finland.
The fresh figures suggest that support for the organization has increased in Sweden by 10 percentage units compared to a previous poll in May, which stated that one in three Swedes favoured membership, up from 29 percent of Swedes in 2013 and 17 percent in 2012.
Political scientist and Social Democrat Ulf Bjereld told the TT newswire late on Sunday that he believes two factors have influenced Swedes' change of heart: a perceived threat from Russia and outgoing Supreme Commander of the Armed Forces Sverker Göranson's comments that Sweden could only defend itself for a week if it were attacked.
“In the past two years we have been seeing a trend that opposition to Nato has decreased,” said Bjereld.
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The Sifo survey was carried out between September 2nd and 8th, after senior figures in two of the parties of Sweden's centre-right opposition – the Centre Party and the Christian Democrats – announced that they would push for membership. The U-turn meant that all four parties in the Alliance, the ruling Social Democrat-Green coalition's main opponents, now support Nato.
“The trend is clear, in particular the Alliance voters are moving towards 'yes',” Toivo Sjörén, head of opinion at Sifo, told Svenska Dagbladet late on Sunday.
Sweden's ruling centre-left coalition – the Social Democrats and the Green Party – remains against Nato. 52 percent of Social Democrat voters said they did not want to join the military organization while 30 percent said they would like to see Sweden becoming part of Nato. The corresponding figures for Green voters were 61 percent against and 27 in favour.
The nationalist Sweden Democrats oppose Nato. However, according to the Sifo poll, 54 percent of the party's voters favour membership.
The results of the poll come just days after Swedish Foreign Minister Margot Wallström called on the Russian ambassador to Sweden to explain controversial comments he made in July, when he said that Sweden would likely face military action if it were to join Nato.
He said at the time that Sweden “was not a target for Russia's armed troops” as long as it remain neutral, but that if it were to join Nato then Russia would adopt “counter measures”.
Although Sweden is set to invest 10.2 billion kronor into its armed forces in the coming year, the country's defence capabilities have been questioned following increasing military activity from Russia in the Baltic region.
In October 2014, a foreign submarine – suspected to be from Russia, although this was never confirmed – was spotted in Swedish waters just outside Stockholm. A number of Russian planes have also been spotted in or close to Swedish airspace over the past year.
There have been indications in the past year that the moves have brought the Nordic country closer to joining Nato. Sweden has previously said it plans to increase its participation in Nato exercises.
In April, Sweden, Norway, Denmark, Finland and Iceland announced far-reaching plans to extend their military cooperation. The move was “a direct response to aggressive Russian behaviour”, said Sweden's defence minister Peter Hultqvist and his Nordic counterparts at the time.