CCPR/C/GC/36 to apply the principles of precaution and proportionality, and the use of human shields would also violate article 6 of the Covenant.259 States parties should, in general, disclose the criteria for attacking with lethal force individuals or objects whose targeting is expected to result in deprivation of life, including the legal basis for specific attacks, the process of identification of military targets and combatants or persons taking a direct part in hostilities, the circumstances in which relevant means and methods of warfare have been used, 260 and whether less harmful alternatives were considered. They must also investigate alleged or suspected violations of article 6 in situations of armed conflict in accordance with the relevant international standards (see paras. 27–28 above).261 65. States parties engaged in the deployment, use, sale or purchase of existing weapons and in the study, development, acquisition or adoption of weapons, and means or methods of warfare, must always consider their impact on the right to life. 262 For example, the development of autonomous weapon systems lacking in human compassion and judgment raises difficult legal and ethical questions concerning the right to life, including questions relating to legal responsibility for their use. The Committee is therefore of the view that such weapon systems should not be developed and put into operation, either in times of war or in times of peace, unless it has been established that their use conforms with article 6 and other relevant norms of international law.263 66. The threat or use of weapons of mass destruction, in particular nuclear weapons, which are indiscriminate in effect and are of a nature to cause destruction of human life on a catastrophic scale, is incompatible with respect for the right to life and may amount to a crime under international law. States parties must take all necessary measures to stop the proliferation of weapons of mass destruction, including measures to prevent their acquisition by non-State actors, to refrain from developing, producing, testing, acquiring, stockpiling, selling, transferring and using them, to destroy existing stockpiles, and to take adequate measures of protection against accidental use, all in accordance with their international obligations.264 They must also respect their international obligations to pursue in good faith negotiations in order to achieve the aim of nuclear disarmament under strict and effective international control,265 and to afford adequate reparation to victims whose right to life has been or is being adversely affected by the testing or use of weapons of mass destruction, in accordance with principles of international responsibility.266 67. Article 6 is included in the list of non-derogable rights in article 4 (2) of the Covenant. Hence, the guarantees against arbitrary deprivation of life contained in article 6 continue to apply in all circumstances, including in situations of armed conflict and other public emergencies.267 The existence and nature of a public emergency that threatens the life of the nation may, however, be relevant to a determination of whether a particular act or omission leading to deprivation of life is arbitrary and to a determination of the scope of the positive measures that States parties must take. Although some Covenant rights other than the right to life may be subject to derogation, derogable rights that support the application of article 6 must not be diminished by measures of derogation. 268 Such rights include procedural guarantees, such as the right to fair trial in death penalty cases, and accessible and effective measures to vindicate rights, such as the duty to take appropriate measures to investigate, prosecute, punish and remedy violations of the right to life. 68. Reservations with respect to the peremptory and non-derogable obligations set out in article 6 are incompatible with the object and purpose of the Covenant. In particular, no reservation is permitted to the prohibition against arbitrary deprivation of life of persons and to the strict limits provided in article 6 with respect to the application of the death penalty.269 69. Wars and other acts of mass violence continue to be a scourge of humanity resulting in the loss of many thousands of lives every year.270 Efforts to avert the risks of war and any other armed conflict, and to strengthen international peace and security, are among the most important safeguards of the right to life.271 70. States parties engaged in acts of aggression as defined in international law, resulting in deprivation of life, violate ipso facto article 6 of the Covenant. At the same time, all States are reminded of their responsibility as members of the international community to protect lives and to oppose widespread or systematic attacks on the right to life,272 including acts of aggression, international terrorism, genocide, crimes against humanity and war crimes, while 14