Related Rule
Practice Relating to Rule 37. Open Towns and Non-Defended Localities
Indonesia’s Air Force Manual (1990) states:
The bombardment of undefended towns, villages and buildings is prohibited if:
(a) there are no armed forces or combatants in these areas;
(b) there are no weapons or other mobile equipment;
(c) there are no installations or permanent military equipment in order to achieve a military purpose;
(d) there is no act of war by the authority or its inhabitants;
(e) there is no activity which supports military operations. 
Indonesia, The Basics of International Humanitarian Law in Air Warfare, Indonesian Air Force, 1990, § 59.