The UK would introduce sanctions against President Putin, the Downing Street said.
British Prime Minister Boris Johnson told his NATO partners on Friday that he was planning "imminent" sanctions against Russian President Vladimir Putin and his Foreign Minister Sergei Lavrov in response to the invasion of Ukraine.
Downing Street said Johnson told his counterparts that Russia's invasion of Ukraine was a "catastrophe" and the Kremlin chief was "engaging in a revanchist mission to overturn post-Cold War order".
Warning that Putin "may not stop there" and calling the situation a "Euro-Atlantic crisis with global consequences", he urged leaders to cut Russia off from the SWIFT international bank transfer system "to inflict maximum pain".
"The UK would introduce sanctions against President Putin and Foreign Minister Sergei Lavrov imminently, on top of the sanctions package the UK announced yesterday," Downing Street said in a read-out of the meeting.
Johnson's comments ratchet up British action this week against Russian interests including banks, businesses and billionaires, though some lawmakers and experts have said the UK is not going far enough.
And it will bring Britain more into line with the European Union, which slapped sanctions on Putin and Lavrov on Friday.
Earlier, Britain and nine other northern European defence allies agreed in a call that further sanctions were needed on Russia after its invasion of Ukraine.
"The leaders agreed that more sanctions were needed, including focusing on President Putin's inner circle, building on the measures that had already been agreed," Johnson told the so-called Joint Expeditionary Force (JEF) bloc according to his office.
The JEF, set up in 2012, is made up of NATO members Denmark, Estonia, Iceland, Latvia, Lithuania, the Netherlands, Norway, and the United Kingdom, and non-members Finland and Sweden.
It is focused on security in the "High North" region around the Arctic, the North Atlantic and the Baltic Sea area.
At a meeting of its defence ministers on Tuesday, they announced upcoming manoeuvres in the Baltic Sea to demonstrate "freedom of movement" in the strategic zone.
Johnson pledged "further UK support to Ukraine" in a phone call with President Volodymyr Zelensky on Friday morning, as Russian forces closed in on the capital, Kyiv.
Britain has said it is ready to provide Ukraine with additional military support including lethal defensive weapons, but Defence Secretary Ben Wallace ruled out sending troops.
He told BBC television that Britain would "hold the line in NATO", adding: "I'm not putting British troops directly to fight Russian troops.
"That would trigger a European war because we are a NATO country, and Russia would therefore be attacking NATO."
Johnson praised "the bravery and heroism of the Ukrainian people in standing up to Russia's campaign of violence", according to Downing Street.
"The Prime Minister committed to provide further UK support to Ukraine in the coming days as the people of Ukraine and the world continue to demonstrate that Putin cannot act with impunity," it added.
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