President Biden remains at his private home in Delaware as the Russian invasion of Ukraine continues to escalate.

Russian President Vladimir Putin raised the alert status for his nuclear forces to "special regime of combat duty" as Russia and Ukraine battle for the fourth day

Putin ordered the Russian defense minister and the chief of the military's General Staff to put the nuclear deterrent forces in a "special regime of combat duty." The move signals tensions could boil over into a nuclear war. 

At the same time, Biden remains at his private residence in Delaware and media communications with the commander-in-chief have slowed to a crawl.

BIDEN SAYS ‘NO-ONE EXPECTED SANCTIONS TO PREVENT ANYTHING FROM HAPPENING,' DESPITE PRIOR WHITE HOUSE CLAIMS

Putin warned last week that countries who interfere with his invasion of Ukraine will face "consequences you have never seen."

Biden and Putin

Presidents Biden and Putin (Chip Somodevilla/Getty Images |  Mikhail Svetlov/Getty Images)

"He is right now threatening a nuclear escalation," said former DIA intelligence officer Rebekah Koffler. "This a veiled threat – or maybe such a veiled threat - he just met with his chief of general staff and minister of defense. He is escalating the conflict into the nuclear domain in order to de-escalate – that is topple Kyiv’s regime quickly."

Turkey has declared that Russia’s actions in Ukraine constitute a war and will act accordingly, Foreign Minister Mevlut Cavusoglu said Sunday.

Pentagon press secretary John Kirby spoke to reporters Friday on the U.S. military's plans to aid Ukraine as Russian forces continue to advance through the country.

One reporter asked Kirby if U.S. intelligence suggests Russian President Vladimir Putin would stop his advancement with Ukraine. Some European countries are anxious that the Russian president's campaign could continue past the borders of the war-torn country. 

"It is not entirely clear if Mr. Putin has designs beyond the Ukraine," Kirby said. "And it's because that's not perfectly clear that we continue to look for ways to bolster our NATO capabilities and to reassure our allies. I mean, one of the reasons we're doing this is because we want to make it clear to him that we will defend every inch of NATO territory."

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During an interview with Fox News Digital at the Conservative Political Action Conference (CPAC), Sen. Bill Hagerty, R-Tenn. said Putin will only respond to "people that show a spine" and stand up to the authoritarian leader, which the U.S. is unfortunately not doing at the moment under Biden's leadership, he said.

Biden in Delaware

President Joe Biden walks his dog Commander in Rehoboth Beach, Delaware, Dec. 28, 2021. (Saul Loeb/AFP via Getty Images)

"I think the thing that will be most potent to stopping the advance right now will be people that show a spine, [such as] people like [Ukrainian] President Zelenskyy is [doing]. The folks that show resolve," Hagerty said. "We’re going to [have to] increase the cost to Putin of moving against Kyiv and against the entirety of Ukraine."

Fox News's Kelly Laco and Emma Colton contributed to this report.