The movements come as Russian President Vladimir Putin has declared a "red line" on further NATO military expansion of installations in Ukraine.
"The point is: It is not a drill," CNA's director of Russia studies Michael Kofman told the Post. "It doesn't appear to be a training exercise. Something is happening. What is it?"
According to the report, social media has shown Russian military trains and convoys moving tanks and missiles in southern and western Russia.
After training exercises, Russia's 41st Combined Arms Army did not return to its home Siberian city of Novosibirsk, and instead joined other Russian forces near the Ukrainian border. Russia's elite 1st Guards Tank Army is moving equipment and forces toward Ukraine, Kofman told the Post, citing satellite imagery.
"I think you have to step back and look at this past year holistically, and if you do, you will know that the Russian tone and messaging on Ukraine has changed dramatically," he explained to the paper.
"It appears that Russia is shifting the goal post of what is acceptable."
According to the Post, Ukraine's National Security and Defense Council Secretary, Oleksiy Danilov, evaluated 80,000-90,000 Russian troops deployed near the Ukraine border and tens of thousands placed in Crimea.
Russian Ministry of Foreign Affairs spokeswoman Maria Zakharova blamed Ukraine for planning to retake the Donbas region by force.
"When the Ukrainian army feels the need to defend its land, it does so, and it will further act under this principle," Ukrainian President Volodymyr Zelensky announced Friday. "We are not mounting an offensive, we are just responding."
Ukrainian Foreign Minister Dmytro Kuleba continued that Russia is "actively spreading fakes about Ukraine allegedly preparing an offensive or other nonsense. For the record, Ukraine does not prepare any offensive in the Donbas."
The U.S. continued in a statement, "Official Russian rhetoric suggesting Ukraine is aggravating the situation is not only misleading, but it also serves to escalate tensions."
Russia's foreign minister laccused Ukrainian leaders on Monday of attempting to drag Moscow into the conflict in eastern Ukraine.
"We observe attempts to carry out provocations, elicit some reaction from the militia and drag Russia into some kind of combat action," Sergei Lavrov told Russia's state television.
Rebels supported by Moscow have been fighting government troops in Ukraine's Donbass region since 2014, shortly after Russia occupied and annexed the Crimea peninsula from Ukraine. Kyiv says at least 14,000 people have been killed.