A regional Ukrainian governor on Tuesday said the Russian bombardment has caused a leak of toxic nitric acid from an industrial facility.
Luhansk Gov. Serhiy Haidai said a Russian air strike on Sievierodonetsk hit a tank with nitric acid at a chemical factory, causing a massive leak of its fumes.
He posted a picture of a huge rose cloud hanging over the city and urged residents not to leave their homes and wear gas masks or make improvised masks from fabric soaked in soda solution.
Sievierodonetsk has been the focus of Russia's offensive in Ukraine's eastern industrial heartland of Donbas.
It has come under intensive artillery barrage and airstrikes as the Russian forces fought Ukrainian troops for control of the city in violent street battles.