Nato must “work quickly” to process Finland’s bid to become a member, Liz Truss has said.
The foreign secretary confirmed that the UK supports the Nordic country’s application to join the military alliance.
Finland, which has an 800 mile border with Russia, has been forced to rethink its policy on Nato membership by the war in Ukraine.
Pekka Havisto, the Finnish foreign minister, said: “By joining Nato, Finland will strengthen its own security and that of all of Europe.
“We are making this historic decision for future generations.”
Sweden is also actively considering applying for Nato membership in light if Russia invasion of Ukraine.
Last week, Boris Johnson signed security and co-operation agreements with both Sweden and Finland.
The prime minister 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’ve been forced to discuss how best to fortify our shared defences against the empty conceit of a 21st century tyrant.”
Nato was formed in 1949 to prevent a resurgence of nationalism and militarism in Europe after two world wars, and to deter the Soviet Union’s expansion.
Its membership has swelled to 30 member nations, and over the 1990s and 2000s its enlargement stretched further east to include the former Soviet republics of Estonia, Latvia and Lithuania.
Article 5 of the Nato constitution says: “An attack against one ally is considered as an attack against all allies.”
Meanwhile, the Ministry of Defence has said Russia has lost around one-third of the ground troops since it invaded Ukraine in February.
“Russian forces are increasingly constrained by degraded enabling capabilities, continued low morale and reduced combat effectiveness., the latest MoD assessment of the war said. “Many of these capabilities cannot be quickly replaced or reconstituted, and are likely to continue to hinder Russian operations in Ukraine.
“Under the current conditions, Russia is unlikely to dramatically accelerate its rate of advance over the next 30 days.”