In total the four regions make up nearly 20% of Ukraine's territory, and signals huge escalation given this week President Vladimir Putin vowed to use “all the means at our disposal” – including the potential of nuclear arms – to defend Russia's “territorial integrity”. Of course, by bringing whole swathes of Ukraine into Russia, Putin effectively issued a 'by all means' declaration for military defense of these territories.
The Ukrainian presidency's office denounced the move as illegal and a “propaganda show”, saying, “Today, there is no legal action called a ‘referendum’ in the occupied territories.” According to a statement by Zelensky adviser Mykhailo Podolyak:
There is only – 1. [A] Propaganda show for z-conscription. 2. The territory of Ukraine that needs an immediate release,” he added, citing the “Z” letter and symbol that has become synonymous with Russia’s offensive.
Ukraine's Western backers have also dismissed the voting as a “sham” – even as there's widespread acknowledgement the results will likely be overwhelming in favor of joining Russia, given these are by and large places of a concentrated pro-Kremlin and Russian speaking population (especially among those Ukrainians who've remained there under Russian occupation).