Russia and the United States faced off on Monday at the UN Security Council over Moscow's troop build-up on the Ukrainian border, as Western nations intensified their high-stakes diplomatic push to avert open conflict in Europe.
With tensions soaring, the US had vowed to push back against any "disinformation" Moscow put forward in one of the most closely watched UN sessions in years.
The US-requested meeting came with fears growing of an imminent incursion into Ukraine, despite Kremlin denials.
US President Joe Biden released a statement as the talks began warning Russia that it was facing harsh reprisals unless it demonstrated openness to a diplomatic solution.
"If Russia is sincere about addressing our respective security concerns through dialogue, the United States and our allies and partners will continue to engage in good faith," Biden said.
"If instead Russia chooses to walk away from diplomacy and attack Ukraine, Russia will bear the responsibility, and it will face swift and severe consequences."
Russia had tried to block the 15-member Security Council from holding the meeting at all -- with its envoy to the UN Vasily Nebenzya accusing the US on Monday of trying to "whip up hysteria" by pushing the debate.
But Washington's UN envoy Linda Thomas-Greenfield said Moscow's troop build-up justified the meeting, and Russia's blocking move was rejected with 10 out of 15 members backing Washington.
"This is the largest... mobilization of troops in Europe in decades," the ambassador said. "And as we speak, Russia is sending even more forces and arms to join them."
She told the Council Russia's military build-up had been paired with "aggressive rhetoric" as part of an escalation often seen from Russia when it seized Crimea in 2014.
And she accused Russia of planning to build its military force in Belarus to 30,000 within weeks as a part of its threat to Ukraine.
'Putin will not stop'
In parallel with the UN meeting, US Secretary of State Antony Blinken was preparing for fresh talks on Tuesday with Russian counterpart Sergei Lavrov -- the latest of a flurry of diplomatic contacts between Moscow, Washington and Brussels over Ukraine, and broader European security concerns.
The US and its allies have ramped up joint efforts to deter any Ukraine invasion, with Washington and London warning on Sunday it would be punished with "devastating" economic sanctions.
In London, Foreign Secretary Liz Truss said Britain would unveil sanctions legislation targeting "a much wider variety" of Russian economic targets.
The Kremlin denounced Britain's move as an "undisguised attack on business," charging: "The Anglo-Saxons are massively ramping up tensions on the European continent."
Analysts say an array of sanctions hitting Russian banks and financial institutions would not only affect daily life throughout Russia but could roil major economies in Europe and elsewhere.
As they work to defuse the crisis, Western leaders have also stepped-up military assistance to Ukraine.
Britain's Prime Minister Boris Johnson, due to speak with President Vladimir Putin this week, announced London is preparing to offer Nato a "major" deployment of troops, weapons, warships and jets.
Nato Secretary-General Jens Stoltenberg welcomed the increased military support while also endorsing London's diplomatic initiative.
