President Joe Biden reached out to Ukraine’s leader Thursday as the United States moved to take a more direct role in diplomacy between that country and Russia, part of a broader effort to dissuade Russia from a destabilizing invasion of its western neighbor.

President Joe Biden on Wednesday ruled out sending US troops to Ukraine to defend the country from a Russian invasion a day after laying out the consequences for such an incursion during a stern phone call with President Vladimir Putin.

President Biden will warn Russian President Vladimir Putin when they speak on Tuesday that if Russia invades Ukraine, the U.S. is prepared to increase its troop presence, capabilities and military exercises on NATO's "eastern flank," a senior administration official told reporters.

Russian officials have denied rumors spread by Western media and the US government that it is planning to invade Ukraine.