Western powers have called on Russia to lower tensions with Ukraine, and backed Kyiv against any threats from Moscow.
US President Joe Biden spoke with UK Prime Minister Boris Johnson, and the leaders of France, Germany and Italy, agreeing to use "all the tools at their disposal" to prevent aggression.
Mr Biden is to speak to Russia's President Vladimir Putin by video call later on Tuesday, reports the BBC.
Russia has boosted its troops near Ukraine's border, prompting fears.
But Moscow says it has no plan to attack Ukraine and has accused Western nations of provocation.
In a conference call on Monday night, the Western leaders discussed their "shared concern about the Russian military build-up", according to the White House.
The five leaders had "reaffirmed their staunch support for Ukraine's territorial integrity", Downing Street said.
The White House said they had formed a joint strategy "to impose significant and severe harm on the Russian economy" should Russia launch an invasion.
According to US media reports, possible measures include restrictions on Russia's banks or its access to global financial payment systems. But officials say Washington is not planning a US military response.
US State Department spokesman Ned Price said how Washington responds would depend on Moscow's actions.
He said: "If Russia chooses to fail to de-escalate, if Russia chooses to move forward with any plans it may have developed to continue its military aggression or to aggress militarily upon Ukraine, to violate Ukraine's sovereignty, its independence, its territorial integrity, we and our allies would be prepared to act, we would be prepared to act resolutely."
Tens of thousands of Russian troops are believed to be massed near Ukraine's borders.
A large part of the recent Russian military build-up is in Crimea, which Russia annexed from Ukraine in 2014.
Troops are also gathering near Ukraine's eastern Donbas region, the name for parts of Luhansk and Donetsk regions under the control of separatists.
Ukrainian officials have said Moscow could be planning a military offensive at the end of January.
But the Kremlin has blamed "aggressive and hostile rhetoric" from Western countries for stoking tensions.
Mr Putin's press secretary, Dmitry Peskov, said the Russian president would "listen with great attention" to Mr Biden's proposals on Ukraine.
"There is only one way to defuse tensions - to understand how to ensure against the possible intentions of Kyiv to solve the Donbas problem through force," he added.