A/HRC/4/40 page 4 Introduction 1. The Working Group on Arbitrary Detention was established by the former Commission on Human Rights in its resolution 1991/42 and entrusted with investigating instances of alleged arbitrary deprivation of liberty, according to the standards set forth in the Universal Declaration of Human Rights and the relevant international instruments accepted by the States concerned. The mandate of the Working Group was clarified and extended by the Commission in its resolution 1997/50 to cover the issue of administrative custody of asylum-seekers and immigrants. The mandate was confirmed by Commission resolution 2003/31 and assumed by the Human Rights Council in its decision 2/102. 2. During 2006, the Working Group was composed of the following experts: − Ms. Manuela Carmena Castrillo (Spain); − Ms. Soledad Villagra de Biedermann (Paraguay); − Ms. Leïla Zerrougui (Algeria); − Mr. Tamás Bán (Hungary); − Mr. Seyed Mohammad Hashemi (Islamic Republic of Iran). 3. Since 4 September 2003, Ms. Leïla Zerrougui has been the Chairperson-Rapporteur of the Working Group and Mr. Tamás Bán the Vice-Chair. I. FIFTEEN YEARS OF WORKING GROUP ACTIVITIES 4. During 2006, the Working Group held its forty-fifth, forty-sixth and forty-seventh sessions. It also carried out official missions to Ecuador (12 to 22 February), Honduras (23 to 31 May), Nicaragua (15 to 23 May) and Turkey (9 to 20 October) (see addenda 2-5 to the current report). 5. In the framework of the review of the mechanisms initiated by the Human Rights Council, the Working Group would like to outline some of the work it has accomplished during the 15 years of uninterrupted activities in the exercise of its mandate. The Working Group is the only non-treaty-based human rights mechanism whose mandate expressly provides for consideration of individual complaints. In addition to the adoption of Opinions on individual cases of detention, the Working Group has also formulated the following Deliberations and Legal Opinions on matters of a general nature, in order to develop a set of guidelines and support States in their efforts to prevent arbitrary deprivation of liberty: − Restricted residence or house arrest (Deliberation No. 1); − Rehabilitation through labour (Deliberation No. 4);