On Monday, US President Joe Biden announced that there are "clear signs" Russia is considering the use of chemical and biological weapons in Ukraine.
With the Russian invasion encountering fierce resistance from Ukrainian fighters, Washington says desperation could push President Putin to resort to drastic tactics.
"The battle lines for Russia are apparently frozen" Samuel Ramani, Associate Fellow at the Royal United Services Institute told Euronews.
The Russian advance in Ukraine appears to have stalled on three key fronts.
"It doesn't seem as if (Russian troops) are making the kind of progress, either in the offensive to capture Kyiv - which is vital for any regime change mission, or in terms of subduing key targets in eastern Ukraine, like Odessa or Mariupol, or in western Ukraine where they've expanded the war to Lviv", said Ramani.
As progress slows on the ground, Russia is turning to precision and hypersonic aerial weapons to eliminate key Ukrainian military infrastructure. Ramani warns that this "opens the door for other non-ground forms of attack, like chemical and biological weapons".
"I think a chemical attack... is probably the most plausible because it's also the most deniable. And it also fits in with Russia's modus operandi in the past".
Chemical weapons were used during the Soviet-Afghan war between 1979-1989, and in Syria in 2013.
Moscow claims that its chemical weapons stores have been destroyed. But President Putin's forces could target existing chemical plants.
"It could simply do something like bomb a federal chemical factory, like its shelling in Sumy over the weekend, and that would make it look like... Ukraine (is) having a chemical leak - but it's actually Russia carrying out an attack".