A freight train moving military equipment associated with a nuclear arms division of Russia's Defense Ministry is reportedly on the move, stoking fears of a possible escalation of President Vladimir Putin's war against Ukraine.

A series of BPM-97 armored personnel carriers and other military vehicles were seen traveling through central Russia in a clip posted Sunday on the Telegram messaging app by pro-Russian channel Rybar, the Daily Mail reported Monday.

The carriers are believed to be upgraded with more turrets, reinforced ambush and mine-proof armor, and an air purification system to allow soldiers to operate even under sustained infantry attacks, the news outlet reported.

The advanced military hardware reportedly belongs to the 12th Main Directorate of the Russian Ministry of Defense — a specialist division dedicated to the storage, maintenance, and provision of weapons that's akin to a Russian military branch controlling nuclear missiles, the Mail reported.

Military analyst Konrad Musyka claimed the deployment of such units could signal an escalation in the conflict — or a precursor to large scale nuclear drills.

It comes as NATO warned member states that Russia's Belgorod nuclear submarine has left its White Sea base, while Putin ally Ramzan Kadyrov said Russia's military should use "low-yield nuclear weapons" to turn the tide of the war in Ukraine, the Mail reported.

Muzyka said though the movement of heavy military hardware belonging to nuke-wielding units doesn't necessarily mean Russia is preparing to deploy a nuclear weapon in Ukraine, it could suggest a "signal to the West that Moscow is escalating" the conflict.

Russia's Strategic Rocket Forces is a branch of Russia's armed forces that constitutes a cornerstone of the nation's nuclear defense and deterrence program — the largest and most advanced in the world.

"We're in a situation in which superiority in resources and conventional weaponry is on the side of the West," Vasily Kashin, a military and political analyst at the Higher School of Economics in Moscow, told the Mail. "But Russia's power is based on its nuclear arsenal."

Concerns over the movement of the 12th Main Directorate's military hardware come as NATO warned that a key Russian nuclear submarine has left its base in the White Sea in northern Russia. The warning note claimed the K-329 Belgorod submarine may be headed to the Kara Sea to test the Poseidon underwater nuclear drone.

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