BRUSSELS — NATO Secretary-General Jens Stoltenberg hailed an "historic moment" on Wednesday after Finland and Sweden formally submitted their applications to join the military alliance.

The seismic shift from long-held neutrality -- which has popular support in both countries -- was spurred by Russia's invasion of Ukraine.

“I warmly welcome the requests by Finland and Sweden to join NATO. You are our closest partners,“ Stoltenberg said.

“All allies agree on the importance of NATO enlargement. We all agree that we must stand together, and we all agree that this is an historic moment which we must seize.”

“This is a good day at a critical moment for our security,” a beaming Stoltenberg said, as he stood alongside Finland's and Sweden's ambassadors to NATO.

Russian President Vladimir Putin has demanded the alliance stop expanding toward Russia's borders, and several NATO allies, led by the United States and Britain, have signalled that they stand ready to provide security support to Finland and Sweden should he try to provoke or destabilise them during the time it takes to become full members.

The countries will only benefit from NATO's Article 5 security guarantee -- the part of the alliance's founding treaty that pledges that any attack on one member would be considered an attack on them all -- once the membership ratification process is concluded, likely in a few months.

The move is one of the biggest geopolitical ramifications of the war and will rewrite Europe’s security map. British Prime Minister Boris Johnson welcomed it in a tweet and said that “Putin’s appalling ambitions have transformed the geopolitical contours of our continent”.

For now, though, the application must be weighed by the 30 member countries. That process is expected to take about two weeks, although Turkish President Recep Tayyip Erdogan has expressed reservations about Finland and Sweden joining.

If his objections are overcome, and accession talks go as well as expected, the two could become members soon. The process usually takes eight to 12 months, but NATO wants to move quickly given the threat from Russia hanging over the Nordic countries’ heads.

Canada, for example, says that it expects to ratify their accession protocol in just a few days — while in the Baltic region, Estonian Prime Minister Kaja Kallas tweeted: “I encourage a rapid accession process. We in Estonia will do our part fast.”

Stoltenberg said that NATO allies “are determined to work through all issues and reach rapid conclusions.”

The fact that the Nordic partners applied together means they won’t be losing time by having to ratify each other's membership applications.

“That Sweden and Finland go hand in hand is a strength. Now the process of joining the talks continues,” Swedish Foreign Minister Ann Linde told the Swedish news agency TT.

It shouldn't take long to win approval in the Baltic states of Estonia, Latvia and Lithuania. Their prime ministers issued a joint statement on Wednesday saying that they “fully endorse and warmly welcome the historic decisions” taken in Helsinki and Stockholm.

Public opinion in Finland and Sweden has shifted massively in favour of membership since Russia invaded Ukraine on 24 February.

Finland and Sweden already cooperate closely with NATO. They have functioning democracies, well-funded armed forces and contribute to the alliance’s military operations and air policing. Any obstacles they face will merely be of a technical, or possibly political nature.

NATO’s membership process is not formalized, and the steps can vary. But first, their requests to join will be examined in a sitting of the North Atlantic Council (NAC) of the 30 member countries, probably at the ambassador level.

The NAC will decide whether to move toward membership and what steps must be taken to achieve it. This mostly depends on how well aligned the candidate countries are with NATO political, military and legal standards, and whether they contribute to security in the North Atlantic area. This should pose no substantial problem for Finland and Sweden.

Moving forward, during accession talks that could be concluded in just one day once the terms of those negotiations are set, the two will be asked to commit to uphold Article 5 and to meet spending obligations concerning the NATO in-house budget, which runs to around $2.5 billion dollars, split proportionally among what would be 32 member countries.

Finland and Sweden would also be made aware of their role in NATO defence planning, and of any other legal or security obligations they might have, like the vetting of personnel and handling of classified information. — Euronews