Соответствующая норма
Practice Relating to Rule 37. Open Towns and Non-Defended Localities
Section C. Attacks on open towns and non-defended localities
In its judgment in the Shimoda case in 1963, Japan’s District Court of Tokyo stated:
Dropping an atomic bomb on undefended towns should … be deemed the same as blind bombing, if it is not an attack on defended towns. Such an act should be recognized as violating international law at that time. 
Japan, District Court of Tokyo, Shimoda case, Judgment, 7 December 1963.