Ukrainian troops on the front lines of the counteroffensive against Vladimir Putin's army are feared to be the most vulnerable should the Russian president decide to finally act on his rhetoric and deploy a tactical nuclear weapon, military experts say.

Nuclear rumors have been gaining in volume during the past several weeks, with officials analyzing various war game scenarios and finding it increasingly likely Putin uses some sort of dangerous weapon, which could even include a tactical nuke, described as a type of "low-yield" nuclear weapon.