A video shared online of a train in Russia carrying equipment belonging to a Russian military unit that handles nuclear weapons should be taken as a message to the West, a military analyst says. The video, which a U.S. official told CBS News could not be independently confirmed, shows an armored personnel carrier with a cannon attached, as well as another vehicle belonging to the unit, being transported on the train, the analyst said.

"Such videos are never released by chance. I'm 100% sure that there was a purpose behind posting or releasing such a video," Konrad Muzyka, an aerospace and defense consultant focused on Russia and Belarus, told CBS News.

Muzyka said that it was highly unusual to see a video of that particular Russian unit, the 12th main directorate of the Russian Ministry of Defense, on the internet.

"This video of a train is a very good example of Russian strategy of trying to increase the pressure on the West and signal its — maybe not necessarily readiness — but willingness to escalate the situation," Muzyka said.

The video surfaced amid reports, which CBS News has been unable to independently verify, that the U.S.-led NATO military alliance had warned its member nations that Russia could be preparing to test its nuclear-capable Poseidon torpedo. The weapon was reportedly on a Russian military submarine headed toward the Arctic. There were also reports in the British press, which Muzyka said were incorrect, that the train featured in the online video was heading toward Russia's border with Ukraine.

"Going forward, we are going to see more reports about Russian activities that relate to nuclear weapons, that relate to drills of units which can potentially be carrying nuclear warheads," Muzyka said. "Russia will try to increase the pressure on the West, and it will try to indicate to the world that, from its point of view, the nuclear option is being considered. But, you know, I still think that, to a large extent, it is a bluff."

Myzyka said that by declaring recently that all options are on the table, the Russian leader has put himself in a position where he "cannot really back down right now. And they will try to test Western resolve, and they will try to influence Western and Ukrainian decision making."

Fears that Russia could launch a tactical, or small-scale nuclear strike have mounted since Putin issued his warning last week that he would defend Russian territory — including parts of Ukraine he unilaterally declared dominion over this week — by "all the means at our disposal."

Ukraine's President Volodymyr Zelenskyy appeared to take the threat seriously, telling CBS' "Face the Nation" on Sunday: "Maybe yesterday it was a bluff. Now, it could be a reality."

"He wants to scare the whole world. These are the first steps of his nuclear blackmail," Zelenskyy said. "I don't think he's bluffing. I think the world is deterring it and containing this threat. We need to keep putting pressure on him and not allow him to continue."

CBS News senior foreign correspondent Charlie D'Agata asked the exiled mayor of Melitopol, a Ukrainian city currently occupied by Russian forces, whether he believed the Russian leader would resort to nuclear weapons as he lashes out in anger over battlefield losses.

"I expect it," Mayor Ivan Federov told CBS News.

Justin Crump, a veteran of the British army and the CEO of the intelligence consulting firm Sibylline, told BBC News earlier Tuesday, however, that Russia was likely stoking concern over a possible nuclear attack primarily to influence Western decision making.

"I think it's pretty clear that Russian intent is to keep us nervous, to try across a whole spectrum of activities to dislocate Western support for Ukraine," Crump said. "I suspect that there's quite a high likelihood of some kind of nuclear test in the Arctic, probably showcasing their new technology. That could well happen at this time of year anyway. But of course, anything like that now will be jumped on as proof that Russia is increasing the tension, increasing the ante, is getting ready to use weapons… These are not things to indicate something is imminent, but they're being jumped on and extrapolated in this climate of fear. So that's something we do have to be quite aware of."

CBS News