Switzerland
Practice Relating to the Use of Prohibited Weapons
Switzerland’s Basic Military Manual (1987) states that “employing methods and means of combat expressly prohibited in the Swiss army” constitutes a war crime. 
Switzerland, Lois et coutumes de la guerre (Extrait et commentaire), Règlement 51.7/II f, Armée Suisse, 1987, Article 200(2)(a).