FINLAND and Sweden are set to join Nato "in months" - doubling the alliance's border with Russia and enraging Vladimir Putin.
The Nordic countries are expected to apply for a fast-tracked membership in the coming days, diplomats and officials have said.
In a joint press statement, Finnish President Sauli Niinisto and Prime Minister Sanna Marin said their country should join Nato "without delay".
"Nato membership would strengthen Finland's security. As a member of Nato, Finland would strengthen the entire defence alliance.
"Finland must apply for Nato membership without delay."
They added: "We hope that the national steps still needed to make this decision will be taken rapidly within the next few days."
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Speaking with , diplomats said that during the one-year ratification process, allied troops would increase in the region and that there would be more military exercises and naval patrols in the Baltic Sea and a rotation with US and Brit forces.
Sweden is also expected to announce its bid on Sunday, overturning decades of opposition to Nato membership.
"Yes and yes: they will apply and they will be granted membership," a senior diplomat told Reuters, on the condition of anonymity.
The move is expected to enrage Russia, which will see itself encircled by Nato territory on its western flank from the Arctic to Turkey.
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It's understood that both countries have been spooked by Mad Vlad's invasion of Ukraine and are seeking security ties with the West to fend off any aspirations by Russia to invade.
"If not now, then when?" said a second diplomat.
A third Nato diplomat said: "It is a blessed moment. Russia is not in a position to attack (the Nordic nations)."
However, envoys fear Moscow could retaliate by moving missiles and other weapons closer to its border with Finland.
Dmitry Peskov, the Kremlin's chief spokesperson, declined to comment on Russia's possible reaction.
"Of course, we observe everything that is connected with actions that are capable of somehow changing the configuration of the alliance near our borders in the most attentive way," he said.
"This is a subject for very, very careful analysis. For now, we can't say any more."
It comes as Prime Minister Boris Johnson yesterday signed historic security treaties with both of the traditionally neutral Scandinavian countries.
The two-fingered salute to the Russian president will see the UK will increase troop presence in both countries and step up intelligence sharing.
Britain will also support joint cyber attack defences, it was agreed, as the countries committed to backing each other at a time of war.
On a whistle-stop tour yesterday of Stockholm and Helsinki — the capitals of Sweden and Finland — Mr Johnson said: “In the event of an attack we will come to the other’s assistance, upon request, and it will be up to the other party to say what kind of assistance they want.”
Pushed on whether or not that would include sending in troops, and risking a conflict with Russia, the PM replied: “In the event of an attack, then yes we will come to each other’s assistance including with military assistance.”
In a warning to the Kremlin, Mr Johnson added: “The many carcasses of Russian tanks that now litter the fields and streets of Ukraine, thanks to Swedish-developed and British-built NLAWS, certainly speak to how effective that co-operation can be.”
Although tiny in population, Finland shares an 830-mile land border with Russia.
The capital Helsinki is just 240 miles from Putin's home city St Petersburg.
And in recent weeks, Russian warplanes have menaced Swedish air space as the country debates joining Nato.
Following talks with Finland President Sauli Niinistö, Mr Johnson said the “solemn declarations” reflect the “extreme difficulty of the times we are in”.
He was greeted by Mr Niinistö for the signing at the Presidential Palace in Helsinki, just hours after putting his name to a pact with Swedish PM Magdalena Andersson at Harpsund, her country retreat near Stockholm.
The pair also took a rowing trip for the cameras, where Mr Johnson joked: “We really are in the same boat now.”
He added: “We are steadfast and unequivocal in our support to both Sweden and Finland and the signing of these security declarations is a symbol of the everlasting assurance between our nations.
“These are not a short-term stop-gap, but a long-term commitment to bolster military ties and global stability and fortify Europe’s defences for generations to come.”
The PM warned Russia’s invasion of Ukraine marked the “end of the post-Cold War” and said it had “sadly opened a new chapter”.
A Kremlin spokesman hit back last night to say Russia was “watching very closely anything that can affect Nato configuration near our borders”.
No10 replied by saying that democratically elected countries, such as Sweden or Finland, could decide their own fates.
Both Mr Johnson and Mr Niinistö were keen to stress that Nato was a defensive organisation and posed no threat to anyone.
Asked whether, joining Nato would provoke more Russian aggression, Mr Niinistö replied; “They are ready to attack their neighbouring country, so my response would be that, ‘You caused this — look at the mirror’.”
Mr Johnson, deploying some of his strongest language yet to condemn the Russian president, said: “This week, many of us have been paying tribute to the brave men and women who secured victory and peace in Europe 77 years ago.
“So, it’s a sad irony that we have been forced to discuss how best to fortify our shared defences against the empty conceit of a 21st century tyrant.”
In the event of an attack, then yes we will come to each other’s assistance including with military assistance.
Boris Johnson
He added: “Most importantly, this is an agreement that enshrines the values that both Sweden and the UK hold dear, and which we will not hesitate to defend.”
Ms Andersson said she was “very happy” to sign the bilateral agreement.
Speaking to the BBC during his visit, Mr Johnson said it was up to the Swedes whether or not they joined Nato, despite keeping neutral throughout the Cold War.
And he hinted: “That may come to a head in the next few days and weeks.
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“It is not for the UK to intervene in that debate. Suffice to say that we would strongly support Sweden’s accession if that was what the Swedes chose to do.
“We would certainly try to make things go as smoothly and easily as possible.”