US President Joe Biden told his Ukrainian counterpart Volodymyr Zelensky in telephone talks on Sunday that Washington and its allies would "respond decisively" if Russia moves to invade its pro-Western neighbor, the White House said.

"President Biden made clear that the United States and its allies and partners will respond decisively if Russia further invades Ukraine," Psaki said in a statement.

Biden also "reaffirmed the United States' commitment to Ukraine's sovereignty and territorial integrity," she said.