Related Rule
Germany
Practice Relating to Rule 13. Area Bombardment
Germany’s Military Manual (1992) states that, when “a number of clearly separated and distinct military objectives located in a built-up area are attacked as if they were one single military objective”, it constitutes an indiscriminate attack and is, as such, prohibited. 
Germany, Humanitarian Law in Armed Conflicts – Manual, DSK VV207320067, edited by The Federal Ministry of Defence of the Federal Republic of Germany, VR II 3, August 1992, English translation of ZDv 15/2, Humanitäres Völkerrecht in bewaffneten KonfliktenHandbuch, August 1992, §§ 454 and 456.