Nato would quickly welcome Finland and Sweden into its ranks if they decide to apply, the military alliance’s top civilian official has said.

It comes as Russia’s war on Ukraine spurs public support in the two Nordic countries for membership.

The military organisation might also be ready to provide security guarantees to the countries if any potential membership bid angers Russia, Nato secretary-general Jens Stoltenberg said.

A poll last month by Finnish broadcaster YLE showed that, for the first time, more than 50% of Finns support joining the western military alliance.

In neighbouring Sweden, a similar poll showed that those in favour of Nato membership outnumber those against.

“If they decide to apply, I expect that all allies will welcome them,” Mr Stoltenberg told reporters in Brussels, as Nato foreign ministers met to discuss the war in Ukraine.

“We know that they can easily join this alliance if they decide to apply.”

Before launching the war on Ukraine, Russian President Vladimir Putin demanded that the 30-nation military organisation stop expanding and pull its troops back from Russia’s borders.

So the prospect of neighbouring Finland, and Sweden, joining is unlikely to be welcomed in Moscow.

To shield them, Mr Stoltenberg said Nato member countries might be prepared to provide a security guarantee to cover the two neutral nations from when they announce a possible membership bid until their applications are endorsed.

Once members, they would benefit from Nato’s collective defence clause, which obliges all members to come to the aid of any ally that comes under attack.

“I am certain that we will find ways to address concerns they may have regarding the period between the potential application and the final ratification,” Mr Stoltenberg said.

He declined to speculate about what those security guarantees might involve.

Finnish foreign minister Pekka Haavisto said his country’s politicians are this month due to debate a government White Paper on security, including an option for Nato accession.

He said Russia’s invasion of Ukraine has changed public opinion.

“In three or four weeks we have a majority, first time ever” in favour of joining, Mr Haavisto said.

He said Finland knows “Russia is ready to take bigger risks, as we can see in Ukraine, bigger risks also for its own security. We can also see that Russia is capable of gathering more than 100,000 men against just one country, even without touching its reserves”.

Mr Haavisto added that “the threshold has been lowered, at least in the debate”, on Russia’s possible use of tactical nuclear or chemical weapons.

He too was reluctant to go into detail about any security guarantee that Finland might need, particularly as debate about joining continues at home.

But Mr Haavisto did say it is something that his country would want to discuss with “key” Nato members, and that Finnish leaders have been in contact with US President Joe Biden and secretary of state Antony Blinken.