President Joe Biden said he believes Vladimir Putin doesn't want full blown war in Ukraine and would pay a "dear price" if he moves forward with a military incursion.
Biden, speaking at a news conference to mark his one-year anniversary in office, also said he believes that Russia is preparing to take action on Ukraine, though he doesn't think the Russian president has made a final decision.
He suggested that he would limit Russia's access to the international banking system if it did further invade Ukraine.
"I'm not so sure that he is certain what is he going to do," Biden said. He added, "My guess is he will move in."
Biden's comments came hours after US Secretary of State Antony Blinken during a visit to Kyiv accused Russia of planning to reinforce the more than 1,00,000 troops it has deployed along the Ukrainian border and suggested that number could double "on relatively short order".
Blinken did not elaborate, but Russia has sent an unspecified number of troops from the country's far east to its ally Belarus, which also shares a border with Ukraine, for major war games next month.
The US president said he believes the decision will "solely" be Putin's and suggested he was not fully confident that Russian officials with whom top White House advisers have been negotiating are fully informed about Putin's thinking.
"There's a question of whether the people they're talking to know what he's going to do," Biden said.
Biden also suggested a "minor incursion" would elicit a lesser response than a full-scale invasion of Ukraine, saying "it's very important that we keep everyone in NATO on the same page."
Biden later in the news conference sought to clarify that he was referring to a non-military action, such as a cyberattack, that would be met with a similar reciprocal response.
Ukraine, meanwhile, said it was prepared for the worst and would survive whatever difficulties come its way. The president urged the country not to panic.
Blinken's visit to the Ukrainian capital came two days before he is to meet in Geneva with Russian Foreign Minister Sergey Lavrov. That follows a series of inconclusive talks last week that failed to ease rising tensions.
Russian military activity has been increasing in recent weeks, but the US has not concluded whether Putin plans to invade or whether the show of force is intended to squeeze the security concessions without an actual conflict.
Biden, who spoke with Putin twice last month, said he's made it clear to him that Russia would face severe sanctions. Still, he said the decision for Putin could come down to "what side of the bed" he wakes up on.
"He's never seen sanctions like the ones I promised will be imposed if he moves, No. 1," Biden warned. "This is not all just a cake walk for Russia," Biden said. "They'll pay a stiff price immediately" and in the medium and long term "if they do it."
In Kyiv, Blinken reiterated Washington's demands for Russia to de-escalate the situation by removing its forces from the border area, something that Moscow has flatly refused to do. And, Blinken said he wouldn't give Russia the written response it expects to its demands when he and Lavrov meet in Geneva.
Meanwhile, a top Russian diplomat said Moscow would not back down from its insistence that the US formally ban Ukraine from ever joining NATO and reduce its and the alliance's military presence in Eastern Europe.
Deputy Foreign Minister Sergei Ryabkov said Moscow had no intention of invading Ukraine but that its demands for security guarantees were non-negotiable.
The US and its allies have said the Russian demands are non-starters, that Russia knows they are and that Putin is using them in part to create a pretext for invading Ukraine, which has strong ethnic and historical ties to Russia. The former Soviet republic aspires to join the alliance, though has little hope of doing so in the foreseeable future.
Blinken urged Western nations to remain united in the face of Russian aggression. He also reassured Ukraine's leader of NATO support while calling for Ukrainians to stand strong.
Blinken told Ukrainian President Volodymyr Zelenskyy that the US and its allies were steadfast in backing his country and its democratic aspirations against Russian attempts to incite division and discord through “relentless aggression." "Our strength depends on preserving our unity and that includes unity within Ukraine," he told Zelenskyy. "I think one of Moscow's long-standing goals has been to try to sow divisions between and within our countries, and quite simply we cannot and will not let them do that."
The Biden administration had said earlier it was providing an additional USD 200 million in defensive military aid to Ukraine. Blinken said more assistance is coming and that it would only increase should Russia invade.
Zelenskyy thanked Blinken for the aid, which was approved in late December but not confirmed until Wednesday.
"This (military) support not only speaks to our strategic plans of Ukraine joining the alliance, but more importantly to the level of our military, our military supplies," he said, referring to Kyiv's desire to join NATO.