Biden tells Zelensky US, allies will 'respond decisively' if Russia invades

President Biden told Ukrainian President Volodymyr Zelensky on Sunday that the U.S. and its allies will "respond decisively" if Russia again invades the so-called Donbas region in southeastern Ukraine.

In a statement, White House press secretary Jen Psaki said the leaders "expressed support for diplomatic efforts," adding that Biden "made clear that the United States and its allies and partners will respond decisively if Russia further invades Ukraine. "

She noted ongoing diplomatic efforts including the bilateral Strategic Stability Dialogue between the U.S. and Russia, as well as discussions through the NATO-Russia Council and the Organization for Security and Cooperation in Europe.

Psaki also reiterated Biden's commitment to Ukraine's sovereignty and territorial integrity.

"President Biden underscored the commitment of the United States and its allies and partners to the principle of 'nothing about you without you,'" she said.

"He also expressed support for confidence-building measures to de-escalate tensions in Donbas," as well as talks between Germany, Russia, Ukraine and France, which also convened in 2014 in an effort to end the war that broke out following Russia's previous invasion of Ukraine.

Biden has recently had conversations with Russian President Vladimir Putin in an effort to lower the tensions between Russia and Ukraine - a videoconference call on Dec. 7 and a phone call on Dec. 31.

Biden warned Putin of severe sanctions should Russia invade Ukraine, while Putin warned that such sanctions would be a "colossal mistake."

Russia has said that it had deployed tens of thousands of troops to its border with Ukraine for its own security, and warned the West against expanding NATO by adding Ukraine.

The U.S. has said it is prepared to supply deadly arms to Ukraine to resist a Russian incursion, along with economic sanctions against Moscow.

Biden discussed his latest call with Putin while speaking to reporters on Dec. 31.

"I made it clear to President Putin that if he makes any more moves, if he goes into Ukraine, we will have severe sanctions," Biden said. "We will increase our presence in Europe with our NATO allies. There will be a heavy price to pay for it."

Updated at 7:52 p.m.