Convention (IV) respecting the Laws and Customs of War on Land and its annex: Regulations concerning the Laws and Customs of War on Land. The Hague, 18 October 1907.
ANNEX TO THE CONVENTION : Regulations respecting the laws and customs of war on land #Section II : Hostilities #Chapter I : Means of injuring the enemy, sieges, and bombardments
Art. 25. The attack or bombardment, by whatever means, of towns, villages, dwellings, or buildings which are undefended is prohibited.