The UK will use “all the economic and diplomatic tools at its disposal” to prevent any invasion of Ukraine by Russia, the Prime Minister has told other world leaders.

Ahead of a key meeting between US President Joe Biden and Russia’s President Vladimir Putin on Tuesday, Boris Johnson spoke to Mr Biden and other leaders to agree on a “united front”.

In the call – which also included Italian Prime Minister Mario Draghi, French President Emmanuel Macron and German Chancellor Angela Merkel – the leaders “reaffirmed their staunch support for Ukraine’s territorial integrity”, a Downing Street spokesperson said.

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Boris Johnson (Christopher Furlong/PA)

And they added: “The Prime Minister said the UK would continue to use all the economic and diplomatic tools at its disposal to prevent any Russian aggression against Ukraine.

“The leaders agreed to speak again following President Biden’s conversation with President Putin tomorrow.”

The US and Russian leaders are due to speak in a video call on Tuesday amid rising tensions over a Russian troop build-up on the Ukrainian border – seen as a sign of a potential invasion.

US intelligence officials have said Russia could be planning for a possible invasion as soon as early next year, while Ukrainian officials have said it could be next month.

A senior Biden administration official said on Monday that Mr Biden will directly address the concerns with Mr Putin.

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US President Joe Biden (Steve Reigate/Daily Express)

He added the president had agreed with European counterparts that there was the option to impose “substantial economic countermeasures by both the Europeans and the United States that would impose significant and severe economic harm on the Russian economy, should they choose to proceed” with an invasion.

Kremlin spokesman Dmitry Peskov confirmed plans on Saturday for the much-anticipated call and said it will take place in the evening.

Russia is adamant the US should guarantee that Ukraine will not be admitted to the Nato military alliance.

Ukraine’s defence minister, Oleksii Reznikov, said the number of Russian troops near Ukraine and in Russia-annexed Crimea is estimated at 94,300, and warned that a “large-scale escalation” is possible in January.

Ukraine’s president, Volodymyr Zelenskyy, recently charged that a group of Russians and Ukrainians planned to attempt a coup in his country and the plotters tried to enlist the help of Ukraine’s richest man, Rinat Akhmetov.

Russia has denied that any plot is under way, but the Russians have become more explicit recently in their warnings to Ukraine and the United States.

The Kremlin said on Friday that Mr Putin, during his call with Mr Biden, would seek binding guarantees precluding Nato’s expansion to Ukraine.

Mr Biden tried to head off the demand in comments to reporters on Friday before leaving for a weekend stay at Camp David.