Boris Johnson warned Vladimir Putin on Wednesday that if his forces attacked Finland or Sweden that Britain would assist in their defence even though they are not currently Nato members.
The Prime Minister signed a mutual security assurance with Prime Minister Magdalena Andersson in Sweden on Wednesday morning, and was later travelling to Finland to sign a similar security declaration with President Sauli Niinistö in Finland.
Speaking at a press conference at Harpsund, the Swedish Prime Minister’s country residence, Mr Johnson told how Britain intends to support the armed forces of Sweden and Finland should either “face crisis or come under attack”.
He explained: “If Sweden were attacked and looked to us for help and support then we would provide it.
“But it is up to Sweden to make the request and to spell out exactly what support is requested,” he added while stopping short of saying whether this would include deploying troops.
He stressed that whether Sweden, or Finland, joined Nato was a separate issue.
As part of the boosted defence co-operation, he also offered to increase deployments to the region, including with Royal Air Force, Army and Royal Navy assets and personnel.
Mr Johnson also held open the door to both nations to join Nato if they wanted to do so.
“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,” he said.
“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.
“Throughout this conflict, our Nordic partners have been leading international support, not just for Ukraine but also for European security,” Mr Johnson added.
“The many carcasses of Russian tanks that now litter the fields and streets of Ukraine thanks to Swedish-developed, British-built NLAWs (Next generation Light Anti-tank Weapon) certainly speak to how effective that co-operation can be.”
The UK is also offering to intensifying intelligence sharing, increase joint military training, exercising and deployments, and work more closely together on hybrid and cyber threats, as part of moves to step up security in northern Europe after Mr Putin’s invasion of Ukraine.
The British security declaration could offer Sweden and Finland reassurance during the period of applying to join Nato, if they do, and actually becoming members when they would get protection under the Article 5 mutual defence arrangements.
Russia is closely watching anything that can affect Nato’s configuration on its borders, Kremlin spokesperson Dmitry Peskov said in response to Mr Johnson visiting Sweden and Finland.
Both countries are expected to make decisions this month on whether to apply to join the Nato military alliance.
The Kremlin has warned them not to and threatened “a military technical response” if they do, stressing the need to “rebalance the situation” in such a scenario.
Mr Johnson will visit Finland on Wednesday afternoon.
The visit came after US intelligence warned Vladimir Putin is preparing for a long war in Ukraine, with even victory in the east potentially not ending the conflict.
Avril Haines, the director of national intelligence, told a US Senate committee hearing yesterday that the Russian leader was still intending “to achieve goals beyond the Donbas”, but that he “faces a mismatch between his ambitions and Russia’s current conventional military capabilities”.
She added the Russian president was “probably” counting on US and EU support for Ukraine to weaken as inflation, food shortages and energy prices got worse.
However, the Russian president could turn to “more drastic means” as the war continues — although Moscow would only use nuclear weapons if Mr Putin perceived an “existential threat” to Russia.
Fierce fighting was continuing on Wednesday in the Donbas region in the east of Ukraine, where Russia has switched its attention after failining in its attempts to seize Kyiv.
Defence intelligence agency director Scott Berrier told the hearing that the Russians and the Ukrainians were “at a bit of a stalemate”.