"As of this moment I am convinced that he has made the decision (to invade)," Biden told reporters in Washington on Friday. "We have reason to believe that," he said, citing US intelligence assessments.
It would occur in the "coming days" and would include an assault on the capital Kyiv, he said.
Biden reiterated his threat of massive economic and diplomatic sanctions against Russia if it did invade, and pressed Putin to rethink his course of action.
He said the United States and its Western allies were more united than ever to ensure Russia paid a price for the invasion.
His comments came after a phone call with the leaders of Canada, France, Germany, Italy, Poland, Romania, Britain, the European Union and NATO, the White House said.
The leaders pledged to continue pursuing diplomacy while preparing to impose swift, co-ordinated economic costs on Russia should it choose further conflict, according to a White House readout of the call.
They also discussed efforts to ensure the defence and security of NATO's eastern flank, the White House said.
Biden's administration has said a diplomatic solution remains possible if Russia chooses, but Washington and its European allies are prepared to enact harsh punishments if Moscow opts to invade.
US Secretary of State Antony Blinken and Russian Foreign Minister Sergei Lavrov planned to meet February 24 in Europe, Biden said, but he warned any Russian military action before that would show Russia has "slammed the door shut on diplomacy".
Meanwhile, US Vice-President Kamala Harris met NATO Secretary-General Jens Stoltenberg at the Munich Security Conference on Friday, expressing concern amid the build-up and vowing to stay in close contact with NATO and US allies.
"We feel very strongly about and will always be committed to the principle of territorial integrity and sovereignty," Harris told reporters.Â
"We remain of course supportive of diplomacy as it relates to the dialogue and discussions we've had with Russia, but we are also committed to taking corrective actions."
Blinken also addressed the conference on Friday, saying Washington remained "deeply concerned" that Russia was planning to attack Ukraine within days.
US Defense Secretary Lloyd Austin also urged de-escalation in a call with his Russian counterpart on Friday, the Pentagon said.
Reuters with AP
