Related Rule
Belgium
Practice Relating to Rule 13. Area Bombardment
Belgium’s Law of War Manual (1983) prohibits “bombardment which treats as a single military objective a certain number of military objectives clearly separated and distinct and located in an area containing a similar concentration of civilian persons and objects”. 
Belgium, Droit Pénal et Disciplinaire Militaire et Droit de la Guerre, Deuxième Partie, Droit de la Guerre, Ecole Royale Militaire, par J. Maes, Chargé de cours, Avocat-général près la Cour Militaire, D/1983/1187/029, 1983, p. 28.