President Biden assured President Volodymyr Zelensky during a call Sunday that the U.S. and its allies will "respond decisively if Russia further invades Ukraine," White House press secretary Jen Psaki said in a statement.

Why it matters: The call is the latest communication between the two leaders ahead of a series of diplomatic talks between Washington and Moscow this month addressing Russia's military buildup along its border with Ukraine.

Driving the news: With Russia moving nearly 100,000 troops near the Ukrainian border, U.S. and European allies have been working to avert a potential large-scale invasion early this year.

What they're saying: "President Biden underscored the commitment of the United States and its allies and partners to the principle of 'nothing about you without you,'" Psaki noted.

• Biden also "reaffirmed the United States’ commitment to Ukraine’s sovereignty and territorial integrity" and expressed support for confidence-building measures to reduce tensions in Donbas, Psaki added.

The big picture: The U.S. and Russia agreed last week to hold bilateral talks on Jan. 10, followed by a meeting of the Russia-NATO Council on Jan. 12 and the Organization for Security and Cooperation in Europe (OSCE) on Jan. 13.

• During a call with Russian President Vladimir Putin on Dec. 30, Biden laid out "two paths" for how the crisis in Ukraine could play out, either via diplomacy or deterrence.
• During a call with Zelensky in early December, Biden "made very clear that one nation can't force another nation to change its borders."

Go deeper: Biden lays out "two paths" for Ukraine crisis in call with Putin