The assessment also said Russia supports more than 35,000 rebels in eastern Ukraine and has about 3,000 of its own military personnel based in rebel territory. Moscow denies having any forces in eastern Ukraine.
"Russia's armed forces appear to have entered their highest level of activity and movement since the autumn-winter build-up began in late October," said an analysis from Janes released Tuesday.
"Evidence indicates activity from all of Russia's major regional commands, and Moscow has also signaled that it will move a large number of surface vessels, including six landing ship tanks (LSTs), a cruiser, and a destroyer, into the Mediterranean Sea, where they could easily continue into the Black Sea."
According to Janes, the force deployed into Belarus from Russia's Eastern Military District is equipped with at least two Iskander-M battalions -- the Iskander being a road-wheeled cruise missile launcher system -- as well as long-range BM-27 multiple rocket launchers, and a large number of main battle tanks.
Russia's Ministry of Defense has also announced the deployment of 12 Su-35S fighter jets, two battalions of S-400 air-defense systems, and a Pantsir-S air-defense battalion to Belarus as part of military exercises there, the analysis said.
Having forces in Belarus helps Russia greatly "because it forces the Ukrainians to defend another several hundred kilometers of border," whether the Russians decide to invade or not, according to Janes. It could also allow the Russians to expand the geographic reach of their radars and electronic warfare systems and bolster their air defenses.
"Units from the Central, Southern, and Western Military Districts appear to be deploying additional equipment, including tanks, artillery, and communications systems, to established sites near the Ukrainian border," the Janes analysis added.
What is Ukraine's military capability?
Ukraine insists that its forces are well prepared. Western allies, including the United States and the United Kingdom, have stepped up their provision of military training, equipment, and supplies to Ukraine as tensions with Russia have risen.
An adviser to Ukraine's President Zelensky told CNN on Wednesday that the US was now providing "an unprecedented level of support" to Ukraine, both military and diplomatic.
"Our army is very well prepared. And you have a population which is very well motivated," Ukraine's Ambassador to Japan Sergiy Korsunsky said this week.
Meanwhile, Zelensky has repeatedly urged Ukrainians to remain calm and not panic.
According to Cranny-Evans, Ukraine's armed forces are in a much better place than they were in 2014 and 2015 when their state of readiness was very low.
"Ukrainian armed forces have really pushed hard for their modernization, they've done what they've can with the domestic industry to improve their capabilities and harden their defenses," he said. "But ultimately, a lot of what they have achieved is tactical in nature. The way in which the Russians fight is very much a level above that."
While nobody really thinks the Ukrainians could stop the Russians, "they've definitely raised the potential costs for the Russian forces," Cranny-Evans added.
"They have the means to really potentially drag Russia into quite a bloody conflict. It's just whether or not Russia can achieve its goals without having to do that."
The ball, at the moment, remains in Putin's court, as the Kremlin leader mulls over written responses by both the United States and NATO to Russia's security demands. As Fiona Hill, who served as the National Security Council's point person on Russia in the Trump administration recently observed in a New York Times op-ed, Putin has a knack for manufacturing crises and can stir up trouble elsewhere around the globe if he wants to further confound Western policymakers.