Russian drones drop caustic and flammable gas on Ukrainian lines to sow panic ahead of conventional shelling, CNN wrote on Dec. 19 in its report on trench warfare on the southern front.
International conventions prohibit the use of chemical agents in warfare, including riot control substances. Ukraine has previously accused Russia of using banned chemical weapons in its full-scale invasion.
Nine gas attacks were reported near Zaporizhzhia Oblast's Orikhiv in recent weeks, resulting in one death, a Ukrainian medic deployed in the sector told CNN.
A Ukrainian intelligence official told the news outlet the substance used was a form of CS gas, a defining component of tear gas, commonly used as a riot control agent.
The substance causes significant irritation of the eyes, mouth, lungs, and skin, and its use in warfare is prohibited under the United Nations' Chemical Weapons Convention.
Two Ukrainian soldiers who survived the gas attack told CNN the substance ignited in their trench.
"The trench was in flames. This gas burns, blinds you, you can't breathe, shoots down your throat immediately. We didn't even have a second."
The two servicemen reportedly suffered burns and welts to their face, mouth, and throat as a result of the exposure.
Oleksandr Tarnavskyi, the commander of the Tavria group of forces, said in August that Russian forces fired artillery barrages with munitions containing a chemical substance, presumably chloropicrin.
Contact with chloropicrin, commonly used during World War I, causes severe irritation to the skin, eyes, and if inhaled, to internal organs.
The Ukrainian military also said in June that Russian forces deployed a gas with suffocating effect near Marinka in Donetsk Oblast, but the wind blew it back in the enemy direction.
A month earlier, Ukraine's Border Service reported that the Russian military had fired munitions with irritant aerosols and chemical grenades near Avdiivka, Donetsk Oblast.