Related Rule
France
Practice Relating to Rule 140. The Principle of Reciprocity
France’s LOAC Teaching Note (2000) states:
Combatants shall respect at any place and in all circumstances the rules of the law of armed conflict … They may in no case release themselves from those rules, regardless of the framework and the mandate of their mission, even if the enemy does not respect those rules. 
France, Fiche didactique relative au droit des conflits armés, Directive of the Ministry of Defence, 4 January 2000, annexed to the Directive No. 147 of the Ministry of Defence of 4 January 2000, p. 7.
France’s LOAC Manual (2001) provides that combatants must respect in all circumstances the rules of the law of armed conflict “even if the adversary does not respect these rules”. 
France, Manuel de droit des conflits armés, Ministère de la Défense, Direction des Affaires Juridiques, Sous-Direction du droit international humanitaire et du droit européen, Bureau du droit des conflits armés, 2001, p. 14.