U.S. President Joe Biden on Thursday said any country that backed Russia's onslaught in Ukraine would be "stained by association," after China rejected calling Moscow's move an invasion and instead urged all sides to exercise restraint.

Ukrainian forces battled Russian invaders on three sides after Moscow mounted an assault on Ukraine by land, sea and air in the biggest attack on a European state since World War Two.

Biden, speaking to reporters at the White House where he unveiled tough new sanctions on Russia coordinated with allies, said Russian President Vladimir Putin's actions represented a dangerous moment for freedom around the world.