Finland and Sweden are strengthening their ties with Nato, in developments prompting Russian criticism and scrutiny.

Known in the Cold War for their neutrality, in 2014 the two Nordic states signed new accords with Nato on so-called host-nation support.

Student or retired? Then this plan is for you.

The agreements enable joint training and military assistance from Nato troops in emergency situations. The accord has already entered into force in Finland. It will be up for a vote in the Swedish parliament on 25 May.

The Finnish government also commissioned a team of independent experts to rate the consequences of possible Nato membership.

The report, put forward on Friday (29 April), said a Finnish application would be a “sea change” in the country's foreign policy, and was likely to upset Russia. It recommended that relations with Nato should be conducted together with Sweden.

"Whatever is done should be done together," said Francois Heisbourg, one of the authors.

The experts noted that Finland took part in the EU’s common security and defence policy (CSDP). But they said the EU policy was complementary to Nato’s military capabilities rather than a potential substitute.

Finland's prime minister Juha Sipila welcomed the report’s findings. He said Finland would let Sweden know if it chose to apply for Nato membership.

"We have promised not to surprise each other in these matters," he said.

Finns haven't forgotten that Sweden applied for EU membership without forewarning its Nordic neighbours, in 1990.

A Russian spy in Sweden?

Norway, Iceland and Denmark are already in Nato.

But Sweden's relations with Russia soured last week when Russia's foreign minister lectured Stockholm on the consequences of joining the Western military alliance.

"We would have to take the necessary defence measures on our northern borders," Sergey Lavrov said in an interview with Dagens Nyheter.

The article was published just a few hours before the Finnish experts’ report.

Lavrov called Russia's response to potential Nato expansion “nothing personal, it’s just business”.

He said Sweden should settle the question through a referendum.

His Swedish counterpart, Margot Wallstroem, replied to him on Twitter, saying: "Nobody but Sweden decides our security policy. Military neutrality has served us well and prevails."

She sent a similar message the next day - this time in English - after Dagens Nyheter published an interview, with Wilhelm Unge, a senior analyst in Sweden’s intelligence service, the Sapo.

He said Russia was behind some of the Swedish dissent against the Nato host-nation pact to be voted later this month.

"At least one conference was attended by a person that we can connect to the Russian intelligence service," Unge said.

He said the person had campaigned against the agreement, but declined to name the spy.

Sweden's minister of defence, Peter Hultquist, said in February that someone was spreading “lies and bloody poems” about the Nato deal.

Sapo estimates that a third of Russian embassy staff in Sweden are involved in activities outside the remit of the Vienna convention on diplomatic relations.

Supo, the Finnish equivalent, also cites Russia as the country most interested in Finnish internal affairs.

Nato support grows

Popular support for Nato has grown in both countries in the wake of Russia’s war on Ukraine.

About one third of Swedes want to join Nato, according to a DN poll, but half of the population is opposed to the idea.

In Finland, the figures are 22 percent for Nato membership and 55 percent against, the public broadcaster Yle said.

Both coalition partners in Sweden - Social Democrats and Greens - oppose Nato membership.

Finland's government will assess the experts’ report in spring as part of a broader foreign policy overhaul.