The two presidents spoke on Sunday just days after President Biden spoke with his Russian counterpart Vladimir Putin for a second time in a month amid tensions along Ukraine’s border.

White House Press Secretary Jen Psaki said the U.S. and its allies would “act decisively” if Russia invaded its neighbor.

In the statement, Psaki said: “President Joseph R. Biden, Jr. spoke today with President Volodymyr Zelensky of Ukraine.

“President Biden made clear that the United States and its allies and partners will respond decisively if Russia further invades Ukraine.

“The leaders expressed support for diplomatic efforts, starting next week with the bilateral Strategic Stability Dialogue, at NATO through the NATO-Russia Council, and at the Organization for Security and Cooperation in Europe.

“President Biden underscored the commitment of the United States and its allies and partners to the principle of ’nothing about you without you.’ He reaffirmed the United States’ commitment to Ukraine’s sovereignty and territorial integrity.

“He also expressed support for confidence-building measures to de-escalate tensions in Donbas and active diplomacy to advance the implementation of the Minsk Agreements, in support of the Normandy Format.”

President Zelensky said about the conversation in a January 2 Twitter post: “The first international talk of the year with @POTUS [President of the United States] proves the special nature of our relations.

“Joint actions of [Ukraine], [U.S.] and partners in keeping peace in Europe, preventing further escalation, reforms, deoligarchization were discussed. We appreciate the unwavering support of [Ukraine].”

The statements come after Russia deployed some 100,000 of its troops along its border with Ukraine, although the country’s defense officials believe the number could be as high as 120,000, according to CNN.

President Biden warned Russia will have a “heavy price to pay” if Moscow orders an invasion of Ukraine and said the U.S. is prepared to issue severe sanctions in response to an attack.

In addition to the U.S., the European Union and NATO have issued warnings to Russia and have called for a de-escalation of tensions along Ukraine’s border.

Meanwhile, Russia’s President Vladimir Putin has warned Washington D.C. that introducing new sanctions would be a “colossal mistake,” according to The BBC.

President Biden’s response to the tense situation has been criticized by Republicans, who have claimed it does little to protect Ukraine.

Representative Jim Jordan (R-OH) said in a December 8 tweet: “President Obama gave Ukraine blankets.

“President Trump gave Ukraine tank-busting Javelin missiles. President Biden waved at the camera.”

Tensions have remained high in Eastern Europe since Russia forcibly annexed the Russian-speaking majority region of Crimea in 2014, in a move that was condemned by Western leaders.

Following the forcible annexation, separatists in the Russian-speaking majority Donbas region have staged an armed conflict with Ukraine, and have been supported by Moscow.

The ongoing conflict has resulted in thousands of civilian and military deaths and has been one of the many issues that have led to a cooling of relations between Moscow and the West.