▶ Watch Video: U.S. warns Russia could be preparing to invade Ukraine

President Biden and Russian President Vladimir Putin will hold a video call on Tuesday, a meeting that comes as U.S. intelligence is warning of a possible Russian invasion of Ukraine as soon as January.

Tens of thousands of Russian troops have amassed at the Ukraine border — months after thousands of troops assembled at the border in the spring. But unlike last spring’s buildup, which was regarded as a show of force, U.S. intelligence officials are warning that this one could be in preparation for an actual incursion into the Donbass region of Eastern Ukraine.

On a call with reporters Monday, a senior administration official didn’t go into specifics about what President Biden will tell Putin the U.S. military will or won’t do in the event of an incursion. The official did said that in the event of a Russian military invasion, the U.S. will provide reassurance to allies.

“I don’t want to use a public press call to talk about the particular sensitive challenges that President Biden will lay out for president Putin, but I would say that the United States is not seeking to end up in a circumstance in which the focus of our countermeasures is the direct use of American military force as opposed to a combination of support for Ukrainian military, strong economic countermeasures, and a substantial increase in support and capability to our NATO allies to ensure that they remain safe,” the official said. 

U.S. President Joe Biden (L) and Russian President Vladimir Putin meet during the U.S.-Russia summit at Villa La Grange on June 16, 2021 in Geneva, Switzerland. Biden is meeting his Russian counterpart, Putin, for the first time as president in Geneva, Switzerland.

Peter Klaunzer – Pool/Keystone via Getty Images

Russia has denied any buildup and has accused Ukraine of its own troop buildup, according to BBC News.

Mr. Biden will speak to key European allies later Monday, and will speak with Ukraine President Volodymyr Zelenskyy after his call with Putin, according to the senior administration official.

Mr. Biden said Friday that he has been “aware of Russia’s actions for a long time.” Putin said last week that he had new “red lines” — Washington and its allies must not deploy missiles in Ukraine capable of hitting Moscow. He is also fiercely opposed to Ukraine’s bid for NATO membership, and has demanded guarantees that the transatlantic military alliance will not push its geopolitical boundaries further east, toward Russian soil.  

Mr. Biden said Friday that he doesn’t “accept anyone’s red lines.”

White House press secretary Jen Psaki on Friday repeated Mr. Biden’s earlier remarks that he is putting together a “comprehensive and meaningful set of initiatives” to European leaders. She said the U.S. is exploring a “range of options.”

“We know what President Putin has done in the past, we see that he is putting in place the capacity to take action in short order, and should he decide to invade, that is why we want to be prepared and in an area where we have expressed serious concern about,” Psaki said. “So, what he means by a group of- a package is there’s a range of tools at our disposal. Of course, economic sanctions are an option.”

A possible Russian invasion of Ukraine could involve as many as 175,000 troops, a U.S. official confirmed last week to CBS News. The plans involve extensive movement of 100 battalion tactical groups with an estimated 175,000 personnel, along with armor, artillery and equipment, according to an administration official. 

Roughly 70,000 Russian troops are currently deployed opposite Ukraine, although they lack the support units needed to launch an invasion. That support would come from reservists. 

U.S. Secretary of State Antony Blinken said Friday that Putin’s actions on the border are “very, very concerning” not just to the U.S. but to European leaders as well. Blinken said there would be “high-impact economic consequences” if Putin stages an incursion into Ukraine.

“Well, we don’t know President Putin’s intent,” Blinken said. “We don’t know if he’s made a decision to take renewed aggressive action against Ukraine.”

In 2014, Russia annexed Ukraine’s Crimea peninsula and amassed troops along the border. Blinken said last month that “our concern is that Russia may make the serious mistake of attempting to rehash what it undertook back in 2014 when it amassed forces along the border, crossed into sovereign Ukrainian territory, and did so claiming falsely that it was provoked.”

Olivia Gazis and David Martin contributed to this report.