President Joe Biden called Ukrainian President Volodymyr Zelenskyy on Sunday to reaffirm the United States' commitment to protect them in the face of a looming invasion from Russia's Vladimir Putin.

The White House released the readout of Biden's call with Zelenskyy where the former stressed that the U.S. is ready to quickly respond to any move Russia makes in invading Ukraine. According to the readout, Biden and Zelenskyy have agreed to diplomatically address Russia regarding the massive troops it has stationed near the Ukrainian border.

"President Joseph R. Biden, Jr. spoke today with President Volodymyr Zelenskyy of Ukraine. President Biden reaffirmed the commitment of the United States to Ukraine's sovereignty and territorial integrity," the readout said.

"President Biden made clear that the United States would respond swiftly and decisively, together with its Allies and partners, to any further Russian aggression against Ukraine. The two leaders agreed on the importance of continuing to pursue diplomacy and deterrence in response to Russia's military build-up on Ukraine's borders," it added.

On Monday, Biden called United Kingdom Prime Minister Boris Johnson to discuss their diplomatic engagements with Russia and Ukraine. They also reviewed "diplomatic and deterrence efforts in response to Russia's continued military build-up on Ukraine's borders." Both leaders affirmed continuous support for the sovereignty and territorial integrity of Ukraine.

They also discussed how to reinforce the "defensive posture on NATO's eastern flank and underlined the continued close coordination among Allies and partners." Both leaders talked about their respective country's "readiness to impose severe consequences on Russia should it choose to further military escalation."

Prior to calling Johnson and Zelenskyy, Biden made efforts to calm tensions between Russia and Ukraine by talking to Putin on Saturday. However, the White House said it wasn't clear if Putin would pursue a diplomatic recourse over a military one.

"But it remains unclear whether Russia is interested in pursuing its goals diplomatically as opposed to through the use of force," the White House said.

During the call, Biden and Putin discussed the "escalating military buildup on the borders of Ukraine." Biden made it clear to Putin that if he persists with an invasion, the United States and its Allies "will respond decisively and impose swift and severe costs on Russia." Biden also pointed out that such a decision from Putin would only produce suffering.

"President Biden reiterated that a further Russian invasion of Ukraine would produce widespread human suffering and diminish Russia's standing. President Biden was clear with President Putin that while the United States remains prepared to engage in diplomacy, in full coordination with our Allies and partners, we are equally prepared for other scenarios," the readout of the call said.

White House Principal Deputy Press Secretary Karine Jean-Pierre, during a briefing on Monday, revealed that intelligence reports anticipate Russia will make the invasion after the Beijing Olympics. Though Jean-Pierre reiterated it could happen anytime since Russia is sending in troops daily at the Ukrainian border in plain sight. Jeanne-Pierre did affirm there are "more than 100,000 troops there" in the border of Ukraine that increase "every day."

"As we have said before, we are in the window when an invasion could begin at any time. We will not comment on any details of our intelligence information except that--except to say that it could begin this week, despite a lot of speculation that it would happen after the Olympics--again, something that Jake Sullivan said right here on Friday," Jean-Pierre said.

"And as we have stated, as Jake Sullivan has stated, that we--in the past 10 days or so, we only continue to see a buildup, not a de-escalation," she stressed.