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. 22. The right of belligerents to adopt means of injuring the enemy is not unlimited.