Russian President Vladimir Putin on Tuesday threatened a "military-technical" response to counter Nato expansion towards Russia’s borders, but said he hoped for a diplomatic solution to rising tension as the US said it was ready to discuss his security demands.
The US and its allies “must understand that we have nowhere to retreat further” and that Russia cannot allow them to deploy missiles in Ukraine that would be a few minutes' striking distance from Moscow, Mr Putin told senior officers on Tuesday at the Russian Defence Ministry.
Russia will “take adequate military-technical response measures and react harshly to unfriendly steps”, he said, underscoring that "we have every right to do so".
His comments came as a top US diplomat said bilateral engagement with Russia will take place in January, but added that Washington would continue to send weaponry and military support to Ukraine if Moscow invades.
"If Russia further invades Ukraine, we will provide additional defensive materials to the Ukrainians, above and beyond that which we are already in the process of providing,” Assistant Secretary of State for European and Eurasian Affairs Karen Donfried said.
“We are poised to move in a dramatic way if Russia does undertake further military aggression against Ukraine," she said in a call with reporters.
The US and Europe accuse Russia of a massive build-up of troops near Ukraine in preparation for a possible invasion as early as next month - something Russia denies.
The US and its allies are working on plans to impose painful new sanctions on Russia if it invades Ukraine. The West has also promised to increase arms supplies to Kiev in the event of a Russian incursion, though Nato has not announced plans for any missile deployments in Ukraine, which is not a member of the alliance.
US President Joe Biden and Mr Putin spoke for two hours by phone this month in an attempt to calm tension and US National Security Adviser Jake Sullivan called his Russian counterpart Yuri Ushakov on Monday.
The Biden administration has already given Ukraine about $450 million in security assistance this year, including Javelin anti-tank missiles, small arms and other lethal and non-lethal gear aimed at boosting Kiev's defensive capabilities.
Ms Donfried, who recently returned from a trip to Moscow, Kiev and Brussels, reiterated that the US is open to dialogue with Russia to de-escalate tension but said talks must include Nato partners and the Organisation for Security and Co-operation in Europe (OSCE).
“Let me be clear: there'll be no talks on European security without Europe. Any dialogue with Russia must address Nato's and others' concerns about Russia's continued threatening behaviour,” she said.
“We will decide on a date together with Russia and we believe that that will take place in January."
Nato's Secretary General Jens Stoltenberg said on Tuesday that though Russia’s military build-up continues, the alliance is ready for dialogue.
“Despite international calls for transparency and de-escalation, the build-up continues. We have made clear that any further aggression against Ukraine would carry a very high price,” Mr Stoltenberg said.
Agencies contributed to this report