British PM has said the UK would support Sweden and Finland should either come under attack during a visit to Sweden.
"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," the prime minister said in a statement issued before he speaks.
Shortly before the conference, a statement from the PM said he would "set out the UK's intention to support the two nations' armed forces should either face crisis or come under attack".
Swedish leader, Magdalena Andersson, also said Sweden would assist the UK should it come under attack. She said Russia had said it would "respond" if Sweden decides to apply to join Nato - but exactly how is unclear.
"The tensions in this part of Europe has increased in the last years given Russia's aggression towards Ukraine," Magdalena Andersson says.
Asked about what support the UK would provide if Sweden was attacked during the Nato joining process, Boris Johnson says: "The declaration makes it clear, it's upon request of Sweden [that] the UK will of course provide assistance."
"What matters primarily is what Sweden decides to request," he adds
The PM says it is a sad irony that EU leaders are being forced to discuss the best way to fortify shared defences against the empty conceit of a 21st Century tyrant.
"When Europe celebrated VE day in 1945, a victory partly ensured by heroism of Russian people, we hoped peace on our continent would endure," he says.
Putin's bloodthirsty campaign against a sovereign nation has put an end to that hope, he says, and made a new reality that we face together.
The BBC's James Landale asks Boris Johnson to spell out exactly what the UK would do if Russia attacked Sweden. Johnson responds by saying that if there was an attack on either of the two liberal democracies then they would come to each other's assistance.
He also says the pact could mean intelligence sharing, or doing joint military exercises together. "It will allow us to share more intelligence, bolster military exercises and further joint development of technology," he says.
"This is an agreement that enshrines the values that both Sweden and the UK hold." He says he is pleased to sign the declaration "that brings our two countries even closer together".
