Biden, Putin hold call amid heightened tensions over Ukraine

President Joe Biden spoke with Russian President Vladimir Putin on Thursday -- their second conversation this month amid heightened fears of a full-scale invasion of Ukraine.

The call, which the Biden administration said comes at Putin's request, was the latest effort to defuse those tensions diplomatically.

But tens of thousands of Russian troops remain near Ukraine's borders, and bellicose rhetoric from Russian officials and state propaganda have Western officials on edge still.

The U.S. and European allies have threatened unprecedented economic penalties for Moscow if it attacks Ukraine, nearly eight years after its forces seized the Crimean Peninsula and sparked a war in Ukraine's eastern provinces known as Donbas.

Sanctions and other penalties have not brought that conflict to an end, with approximately 14,000 people killed and Russian-led separatists still fighting Ukrainian forces. U.S. officials say it's unclear if Putin has decided to attack again in an all-out invasion, but Biden has already made clear U.S. forces will not come to Kyiv's aid on the battlefield.

Instead, the Biden administration is hoping deterrence and diplomacy will stop Putin. A senior administration official said they "cannot speak to why the Russian side has requested the call," but added both leaders believe there is "genuine value in direct leader to leader engagement."

"I think we are at a moment of crisis and have been for some weeks now given the Russian build-up and that it will take a high level of engagement to address this and to try to find a path of de-escalation," the official told reporters Wednesday.

In addition to the leaders' call, U.S. and Russian diplomats will meet on Jan. 10, the two sides confirmed Tuesday, to discuss stated security concerns on either side.

"Open lines of dialogue, open lines of diplomacy have the potential to be constructive as we seek to de-escalate the potential for conflict in and around Ukraine," State Department spokesperson Ned Price said of the talks.

After those meetings, NATO will hold a meeting with Russia on Jan. 12, while the Organization for Security and Cooperation in Europe, a key security forum that has deployed a war monitor in eastern Ukraine, will hold a session Jan. 13.

"The Biden administration continues to engage in extensive diplomacy with our European allies and partners, consulting and coordinating on a common approach in response to Russia's military build-up on the border with Ukraine," Emily Horne, Biden's National Security Council spokesperson, said in a statement.

But some European allies have called for greater involvement. The European Union "must be involved in these negotiations," its top diplomat, Josep Borrell, told the German newspaper Die Welt.

"It's about us. This is not simply the case for two states, i.e. America and Russia, or NATO and Russia -- even if Moscow imagines it," he added in the interview, published Wednesday.

Secretary of State Antony Blinken has said repeatedly the U.S. will not negotiate any arrangement about European security without first consulting European allies -- speaking again to Ukrainian President Volodymyr Zelenskiy Wednesday, just as the two spoke before Biden and Putin's first call this month.

He reiterated "unwavering" U.S. support for Ukraine, per Price, and "discussed efforts to peacefully resolve the conflict in eastern Ukraine and upcoming diplomatic engagements with Russia" -- a nod to both Thursday's call and the Jan. 10 meetings.

Zelenskiy tweeted that he was assured of "full" U.S. support "in countering Russian aggression." U.S. officials have already publicly rebuked Russia's demand heading into talks -- that Ukraine be barred from NATO membership, saying the Western alliance's military activity in former Soviet states threatens Russia.

But other items on Russia's public demands are not "unacceptable" and could be addressed through diplomacy, Blinken, Price and others have said -- provided that Russia de-escalate as well by pulling back its forces from Ukraine's borders.

Instead, while Russian state media reported Monday that more than 10,000 were withdrawn, the senior administration official said there's still a "significant Russian troop presence in and around the border."

The ominous language from Russian officials has also continued. Putin himself said Sunday that he is weighing "diverse" military and technical options if Russia's demands aren't addressed.

Amid that heightened threat, the U.S. Embassy in Kyiv is making "emergency preparations" in case it evacuates non-emergency personnel or diplomats' families, according to internal emails obtained by ABC News.

The embassy is seeking additional security staff to temporarily fill in next month, as the "permanent staff continue Emergency Preparations in case of Authorized or Ordered Departure" -- when an embassy allows diplomats' families and non-emergency personnel to relocate because of a threat.

A State Department spokesperson confirmed Wednesday they are "conducting normal contingency planning, as we always do, in the event the security situation severely deteriorates." But they told ABC News they are not "currently considering evacuations of U.S. government personnel or American citizens from Ukraine."

Russian presidential aide Yuri Ushakov said that during Biden's call with Putin, Biden assured that the U.S. is not going to deploy offensive strike weapons in Ukraine.

"President Biden has clearly stated that the United States does not intend to deploy offensive strike weapons in Ukraine. Our president noted that this is one of the key points that are just included in our documents that we have handed over to the Americans and on which we want to continue substantive negotiations," Ushakov told reporters after a telephone conversation between the presidents.

According to Ushakov, Putin said Russia will seek guarantees of its security.

"Vladimir Vladimirovich Putin outlined in detail the basic principles that were laid down in the documents we submitted, and stressed that negotiations on these three tracks are important for us, of course, but the main thing is that we need a result, and we will achieve a result in the form of ensuring guaranteed security of Russia," Ushakov told reporters. "The US President, in principle, agreed with this point of view and reacted quite logically and quite seriously."

Earlier this month, the State Department updated its travel advisory for Ukraine to include a warning about "increased threats from Russia." The advisory had been at the agency's highest level, "Level 4: Do Not Travel," for months because of the COVID-19 pandemic, but it now warns, "U.S. citizens should be aware of reports that Russia is planning for significant military action against Ukraine."

White House Press Secretary Jen Psaki issued a short statement Thursday following Biden's call with Putin, saying Biden "urged Russia to de-escalate tensions with Ukraine," and "made clear that the United States and its allies and partners will respond decisively if Russia further invades Ukraine."

"President Biden also expressed support for diplomacy, starting early next year 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 reiterated that substantive progress in these dialogues can occur only in an environment of de-escalation rather than escalation," Psaki said.

Also on Thursday, a senior White House official gave a readout of the call between Biden and Putin, saying the tone was "serious and substantive."

According to the official, Biden outlined two paths forward -- all depending on how Russia chooses to proceed.

"President Biden laid out two paths. Two aspects of the US approach that will really depend on Russia's actions in the period ahead. One is a path of diplomacy, leading toward a de-escalation of the situation, and the other is a path that's more focused on deterrence, including serious costs and consequences should Russia choose to proceed with a further invasion of Ukraine," the official said.

"Those costs include economic costs include adjustments and augmentations of NATO force posture in allied countries and include additional assistance to Ukraine to enable it to further defend itself in its territory. as we've laid out previously," the official added.

When asked if Putin had offered any further clarity on if he had made a decision on whether or not to further invade Ukraine, the official said there were "certainly no declarations to intention" in the conversation, but the U.S. will continue to monitor the situation to be ready for whatever Putin decides.

ABC News' Christine Theodorou contributed to this report.