Annex to the Convention: Regulations respecting the laws and customs of war on land - Section III: Military authority over the territory of the hostile state - Regulations: Art. 43.
Art. 43. The authority of the legitimate power having in fact passed into the hands of the occupant, the latter shall take all the measures in his power to restore, and ensure, as far as possible, public order and safety, while respecting, unless absolutely prevented, the laws in force in the country.