A/HRC/19/57 75. Moreover, the Working Group considers of utmost importance effective followup to its country visits and requests the support of Member States therein. Furthermore, it emphasizes the importance of the follow-up to and implementation of recommendations contained in the Working Group’s Opinions. 76. The Working Group takes the opportunity to reiterate the exceptional character of the measure of detention under international human rights law. Article 9, paragraph 3, of the International Covenant on Civil and Political Rights sets forth narrowly circumscribed principles for detention on a criminal charge so as to avoid unlawfulness and arbitrariness. The Working Group emphasizes that the notions of a promptness and reasonableness of pretrial detention are to be construed restrictively. The time period referred to in article 9, paragraph 3, shall be no longer than a few days. Whenever possible States shall seek to ensure that measures less restrictive than detention are available so as not to undermine the very core of the human right to liberty and freedom of movement. States are to ensure that these measures are absolutely necessary and proportional to the objective sought. 77. With respect to habeas corpus, the Working Group recognizes its existence as a self-standing human right. It lies at the core of combating and preventing the phenomenon of arbitrary deprivation of liberty. The Working Group has consolidated its understanding of the scope and effect of habeas corpus through its Opinions and country visits. It reiterates that the right to habeas corpus is not subject to any exceptions or derogations even in the context of armed conflict. Habeas corpus constitutes the ultimate guarantee of individual liberty and provides the possibility to contest the legality of any form and measure of deprivation of liberty. 78. Finally, the Working Group notes with satisfaction the increasing crossfertilization between its activities and the work of other United Nations bodies as well as international and regional instruments for the promotion and protection of human rights. In this context, the ongoing preparation of Deliberation No. 9 will draw upon the statements by other bodies and the Working Group’s own practice on what constitutes detention, the legality requirement and the prohibition of arbitrariness, in pre- and post-trial detention and during the trial. The deliberation is intended to contribute to a harmonious interpretation of human rights norms and standards applicable to deprivation of liberty under customary international law. Collaboration of States and civil society in this context is essential to a successful outcome of the study. V. Recommendations 79. So that it can report more systematically and comprehensively, the Working Group reiterates its proposal to the Human Rights Council to expand the mandate of the Working Group to include the examination of conditions of detention around the world and the monitoring of States’ compliance with their obligations concerning all human rights of detained and imprisoned persons. The mandates of the African Commission’s Special Rapporteur on Prisons and Conditions of Detention in Africa and the Rapporteur on the Rights of Persons Deprived of Liberty of the InterAmerican Commission on Human Rights might provide some guidance as to what could be the scope of such an extended mandate. 80. In the light of the exceptional nature of the pretrial detention measures, the Working Group requests States to ensure that measures alternative to detention and less restrictive in character are available in domestic legal systems. At the same time, 24