Boris Johnson has welcomed fresh impetus to exclude Russia from the Swift global banking system after Germany dropped its opposition to the plan.
In a dramatic move, Chancellor Olaf Scholz also announced Berlin would start sending arms to the beleaguered Ukrainian military.
It marked a reversal of Germany’s long-standing policy of not sending lethal weaponry to conflict zones.
In a telephone call between Mr Johnson and Ukrainian President Volodymyr Zelensky, the two leaders welcomed the “increased willingness” internationally to take action against Russia on Swift.
“The leaders agreed on the need for the international community to isolate Russia completely diplomatically and financially,” a No 10 spokeswoman said.
Mr Zelensky welcomed Britain’s commitment to send more arms, including ammunition and anti-tank weapons, to support the Ukrainian forces in their fight against the Russian invader.
He said on Twitter that they had “agreed on further joint steps to counter the aggressor”.
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