Boris Johnson has promised the UK will not hesitate to protect Sweden if it was attacked by Russia, describing Vladimir Putin as a "21st Century tyrant".
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Mr Johnson went on to sign a similar agreement with Finland - as both nations consider whether to join Nato.
The prime minister insisted the alliance was “more important than ever”.
But just how vital is Nato - and how might President Putin react to its expansion?
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(Subscribe: https://bit.ly/C4_News_Subscribe)
Mr Johnson went on to sign a similar agreement with Finland - as both nations consider whether to join Nato.
The prime minister insisted the alliance was “more important than ever”.
But just how vital is Nato - and how might President Putin react to its expansion?
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Follow us on Instagram - https://www.instagram.com/Channel4News