WASHINGTON: Joe Biden spoke with his Ukrainian counterpart Volodymyr Zelensky late Wednesday night in Washington, the White House said, with the US president vowing "support and assistance."

The conversation came soon after Russia launched an attack on Ukraine overnight, with explosions heard in multiple parts of the country.

"We will continue to provide support and assistance to Ukraine and the Ukrainian people," Biden said in a statement.

Russia says it takes out Ukraine's air defences, air bases

Biden condemned the "unprovoked and unjustified attack by Russian military forces," adding that Zelensky requested the US president "call on the leaders of the world to speak out clearly" against Russian President Vladimir Putin's "flagrant aggression."