US President Joe Biden is due to hold talks with Ukrainian President Volodymyr Zelensky on Sunday, after speaking with Russian President Vladimir Putin.
During the call, Biden plans to raise the massing of Russian troops near the Ukrainian border, the White House said on Friday, adding that he is also due to discuss preparations for planned talks with Moscow to help defuse the conflict.
Biden also plans to reiterate his support for Ukraine's territorial integrity and sovereignty, the White House said.
On Thursday, Biden spoke with Putin over the phone for almost an hour, addressing the Ukraine conflict among other key topics.
The call came ahead of talks in Geneva on January 9 and 10, during which diplomats from both countries will meet to discuss the stand-off. Russia and NATO are planning hold separate talks two days later, on January 12.
For weeks, the West has been concerned about reports that Russia has massed tens of thousands of soldiers in areas not far from Ukraine, triggering fears of a Russian invasion.
Russia rejects the charge, and in turn accuses Ukraine of having moved more soldiers to the eastern areas held by pro-Russian separatist.
The developments recall the events of 2014, when Russia annexed Ukraine's Crimean peninsula and began its ongoing support for separatists in eastern Ukraine.
