It can be called war crime or an act of terrorism, but it certainly seems to violate very many of the laws of war. For example
Rule 15. In the conduct of military operations, constant care must be taken to spare the civilian population, civilians and civilian objects. All feasible precautions must be taken to avoid, and in any event to minimize, incidental loss of civilian life, injury to civilians and damage to civilian objects.
https://ihl-databases.icrc.org/en/customary-ihl/v1/rule15
Rule 71. The use of weapons which are by nature indiscriminate is prohibited
https://ihl-databases.icrc.org/en/customary-ihl/v1/rule71
Rule 19. Each party to the conflict must do everything feasible to cancel or suspend an attack if it becomes apparent that [...] the attack may be expected to cause incidental loss of civilian life, injury to civilians [...] which would be excessive in relation to the concrete and direct military advantage anticipated
https://ihl-databases.icrc.org/en/customary-ihl/v1/rule19