A "nitric acid tank" at a chemical plant in Severodonetsk, eastern Ukraine, was "hit" by a Russian strike on Tuesday, regional governor Sergei Gaïdaï announced, calling on residents to do not come out of air-raid shelters.

• Read also: [LIVE] 97th day of war in Ukraine: here are all the latest developments

• Read also: Ukraine: "most" of Severodonetsk under Russian control

• To read also: “A few thousand” of alleged war crimes identified in the Donbass

“Do not leave the shelters” and “prepare face masks soaked in a soda solution”, wrote the governor on Telegram, recalling that nitric acid could in particular cause lung damage or loss of vision.

In early April, the official had already reported a strike that hit a nitric acid tank in Roubijné, a few kilometers further north of Severodonetsk.

The pro-Russian separatists for their part indicated that a container with nitric acid had “exploded” in the Azot factory in Severodonetsk.

“At the Azot chemical plant, a container with chemicals exploded. According to preliminary information, it is nitric acid. The territory of the factory is still controlled by formations of the Ukrainian regime”, wrote on Telegram Rodion Miroshnik, representative of the separatist republic Lugansk in Russia.

His message was accompanied by a photo showing a thick reddish cloud rising in the sky.

Nitric acid is "dangerous to health (generally reversible lesions)", but can cause death, writes the French society of emergency medicine.

In gas form, it is "suffocating, irritating, even corrosive" when inhaled, and can also affect the skin or eyes.

The city of Severodonetsk, administrative center of the Lugansk region for the Ukrainian authorities has been the epicenter for several days of fierce fighting between the Russian and Ukrainian armies.

“Unfortunately, today Russian soldiers control most of the city,” said Serguiï Gaïdai, in a video Tuesday evening.