First, it was about blowing up a dam, now it’s about unleashing a “dirty bomb.”

A sudden flurry of Russian accusations about supposed Ukrainian plans has fueled new Western fears that President Vladimir Putin might be planning his own escalation to change the course of a war that reached eight months Monday and has not been going his way.

Putin’s embattled defense chief was busy this weekend making phone calls to Kyiv’s closest allies to voice Moscow’s latest evidence-free allegations.

Sergei Shoigu warned defense officials in France, Turkey, Britain and the United States that Ukraine was preparing a provocation and the use of what he termed a “dirty bomb.” The situation is steadily trending toward “a further, uncontrolled escalation,” he warned in one of the calls without elaborating.

It comes after Russia’s new chief commander in Ukraine warned last week that Kyiv could resort to “prohibited methods of war” as Russia faces a retreat in the southern region of Kherson after a slew of humiliating military setbacks. Gen. Sergei Surovikin specifically warned that Ukraine was preparing to attack a key dam in the region, threatening to flood the area.

But Ukraine and its allies have vociferously rejected the Russian accusations, countering that, in fact, the Kremlin’s public claims suggest it is seeking to build a pretext for an escalation, and may be planning a “false flag” operation in which it blames Kyiv for its own actions.

Military analysts said that while concerning, the Russian claims were more likely a desperate attempt to convince the West it was willing to resort to such a drastic step than a sign it was actually planning one.

“This is classic Russian ‘vranyo’ — a lie that I know you don’t believe, and I don’t believe it either. We both know that. But this is my story and I’m sticking to it,” Michael Clarke, a professor of war studies at King’s College London, told NBC News. “So it’s a clumsy double bluff,” he said, “trying to make the West frightened of pushing Moscow too hard.