The US and its allies will “respond decisively” if Russia invades Ukraine,

President Joe Biden told his counterpart in Kyiv as tensions mounted over Moscow’s troop deployments.

The call on Sunday between Biden and Ukraine’s president Volodymyr

Zelensky was the latest diplomatic attempt to allay mounting tensions after Russia amassed about 100,000 soldiers on Ukraine’s eastern frontier.

Washington, Moscow and Nato member states are set to meet for talks in early January, when Russia intends to press for “security guarantees” to limit the military alliance’s expansion in Europe.

Biden “reaffirmed” America’s commitment to Ukraine’s “sovereignty and territorial integrity”, according to a statement by Jen Psaki, White House press secretary.

After the exchange, Zelensky wrote on Twitter that the leaders had discussed “joint actions” by Ukraine, the US and partners “in keeping peace in Europe, preventing further escalation, reforms, de-oligarchisation”.

Biden’s message to Zelensky echoed a telephone conversation last week with Russia’s President Vladimir Putin, in which the US president said Washington and its allies were prepared to respond “decisively” should Moscow invade Ukraine.

A day after the call with Putin, which was arranged last Thursday at Moscow’s request, Biden said: “I’m not going to negotiate here in public, but we made it clear that he [Putin] cannot — I emphasize cannot — move on Ukraine”.

Although the Russian leader has previously denied any plan to invade Ukraine, he said last month he was prepared to use “appropriate military-technical measures” and “react harshly to hostile steps” should Kyiv and its western backers ignore Moscow’s “red lines”.

Russian forces in March 2014 forcibly seized Ukraine’s Crimean peninsula after a pro-democratic movement ousted pro-Moscow president Viktor

Yanukovich. An armed uprising erupted a month later in Ukraine’s two easternmost regions of Donetsk and Luhansk, with Russian-led forces taking over parts of the area.