The centre-left Social Democrats, led by Swedish Prime Minister Magdalena Andersson, has historically opposed NATO membership but the more than six-week conflict has reignited debate in the Scandinavian kingdom.

A policy reversal for the party, which ruled for an uninterrupted 40 years between the 1930s and 1970s, would be historic and could pave the way for Sweden to apply to join NATO.

The issue is expected to be a central to parliamentary elections scheduled for September 11. Neighbouring Finland, which shares a border with Russia, is gearing up for a similar policy decision by early summer.

Sweden is officially non-aligned militarily, although it is a NATO partner and abandoned its position of strict neutrality after the end of the Cold War.

Having initially stressed that non-alignment had "served Sweden's interests well," the prime minister conceded that she was ready to discuss the policy and in late March said she "did not rule out" a bid to join NATO.

The debate, open to all party members, will be "a broader discussion than the question of a yes or no to NATO membership," said Tobias Baudin, Social Democrats secretary general.

The "security policy dialogue" should be completed before the summer, he said.

Support for NATO membership has almost doubled since Russia's invasion of Ukraine, jumping to around 50 percent in Sweden and 60 percent in Finland, according to opinion polls.

Conservative Ulf Kristersson, leader of Sweden's right-wing opposition, has already announced his intention to file a membership application if he were to command a parliamentary majority after September's elections.

The far-right Sweden Democrats, the third-largest party in the 2018 elections, has also touted the idea of membership, after previously being opposed.