52 INTERNATIONAL LEGAL PROTECTION OF HUMAN RIGHTS IN ARMED CONFLICT In relation to international humanitarian law, some individual norms provide in certain circumstances for the possibility of exceptions to the normal obligations. Sometimes a measure is admissible if it is necessary for security reasons65 or when a “grave emergency involving an organized threat to the security of the Occupying Power” exists.66 While civilians, unlike combatants, may normally not be interned, a belligerent may intern protected civilians when its security “makes it absolutely necessary”67 and an occupying Power may do so for “imperative reasons of security”.68 A State may refuse individual relief consignments for “imperative reasons of security.”69 States may subject the activities of relief organizations to measures they “consider essential to ensure their security.”70 Other obligations may be derogated from for “imperative military reasons”,71 when it is “rendered absolutely necessary by military operations”72 or where an “unavoidable military necessity” exists.73 3.  Reservations to international humanitarian and international human rights treaty obligations It is established practice in international law that States, under certain circumstances, may at the time of ratification limit the applicability of a given provision in the treaty by lodging a reservation. According to the Vienna Convention on the Law of Treaties, reservation means “a unilateral statement, however phrased or named, made by a State, when signing, ratifying, accepting, approving or acceding to a treaty, whereby it purports   Geneva Convention IV, art. 27.   Ibid., art. 75. 67   Ibid., art. 42. 68   Ibid., art. 78. 69   Ibid., art. 62. 70   Ibid., art. 142, and Geneva Convention III, art. 125. 71   Geneva Convention IV, art. 49. 72   Ibid., art. 53. 73   1954 Hague Convention for the Protection of Cultural Property in the Event of Armed Conflict, art. 11.2. 65 66