Соответствующая норма
Cambodia
Practice Relating to Rule 74. Chemical Weapons
In 1991, it was reported that in Cambodia “the Phnom Penh government accused the guerrillas of using chemical weapons for the first time in the 12 year-old civil war, by referring to artillery shells containing ‘toxic substances’ being fired”. 
Asian Yearbook of International Law, Vol. 1, 1991, p. 353.