E/C.12/UKR/CO/6 limited to Crimean Tatars, persons with disabilities, persons living with HIV/AIDS and non-citizens. In so doing, the State party should ensure due respect for the principles of confidentiality, informed consent and voluntary self-identification of persons as belonging to a particular group. 29. The Committee encourages the State party to sign and ratify the Optional Protocol to the International Covenant on Economic, Social and Cultural Rights. The Committee also encourages the State party to consider signing and ratifying the International Convention on the Protection of the Rights of All Migrant Workers and Members of Their Families and the International Convention for the Protection of All Persons from Enforced Disappearance, as well as the individual complaint mechanisms under various core human rights treaties which it has not yet accepted, with a view to further strengthening the protection of human rights by providing rights holders with additional opportunities to claim their rights at the international level when domestic remedies have been exhausted. 30. The Committee requests the State party to disseminate the present concluding observations widely at all levels of society, particularly among government officials, members of the Verkhovna Rada and judicial authorities, and to inform the Committee in its next periodic report on all steps taken to implement the present concluding observations. It also encourages the State party to engage nongovernmental organizations and other members of civil society in the process of discussion at the national level prior to the submission of its next periodic report. 31. The Committee invites the State party to submit its common core document in accordance with the harmonized guidelines on a common core document (HRI/GEN/2/Rev.6, chap. I). 32. The Committee requests the State party to submit its seventh periodic report, prepared in accordance with the revised reporting guidelines of the Committee adopted in 2008 (E/C.12/2008/2), by 30 May 2019. 11