Biden assures Ukraine president US will respond 'swiftly' to Russian aggression

President Joe Biden spoke with Ukraine President Volodymyr Zelensky on Sunday to assure him the U.S. would respond to Russian aggression.

President Joe Biden assured Ukrainian President Volodymyr Zelensky that the United States and its allies will respond "swiftly and decisively" to any further aggression by Russia against Ukraine, according to a White House readout of a phone call between the two leaders.

The Sunday morning call took place as U.S. officials continue to warn that an attack from Russia could come "any day now" and urge all Americans still in Ukraine to leave the country.

"President Biden made clear that the United States would respond swiftly and decisively, together with its allies and partners, to any further Russian aggression against Ukraine," the White House said of the call. "The two leaders agreed on the importance of continuing to pursue diplomacy and deterrence in response to Russia's military build-up on Ukraine's borders."

In a tweet Sunday following the call, Zelensky said he and Biden discussed "security, economy, existing risks, sanctions and Russian aggression."