CDL-AD(2006)009 - 30 - 127. While no such responsibility applies if the detention is carried out by foreign authorities without the territorial State actually knowing it, the territorial State must take effective measures to safeguard against the risk of disappearance and must conduct a prompt and effective investigation into a substantiated claim that a person has been taken into unacknowledged custody. 128. The possible obligation by a Council of Europe member State under bilateral or multilateral treaties to co-operate in prosecution measures does not affect or diminish this State’s obligation not to allow or contribute to secret detention on its territory. 129. As the European Court of Human Rights has pointed out83, the opinion of the State under whose authority the detention is decided and executed concerning the issue of whether the detention is in violation of fundamental rights is not conclusive for the question of whether cooperation engages responsibility of a member State of the Council of Europe under the European Convention on Human Rights; only the relevant provisions of the latter Convention, as interpreted by the European Court of Human Rights, are decisive. This means, for instance, that the opinion which has been put forward in certain quarters with respect to the US Government that “cruel and unusual punishment”, if applied outside US territory, does not violate the US Constitution, is of no relevance whatsoever for the question of responsibility of member States under the European Convention on Human Rights. It also means that the individual opinion of specific Governments, or of certain public persons, about possible limits to the absolute character of the scope of the prohibition of torture are not relevant either. In addition to the interpretation given by the European Court of Human Rights concerning the absolute character of the prohibition of torture, Article 2, paragraph 2, of the UN Convention against Torture and Other Cruel, Inhuman or Degrading Treatment or Punishment expressly states that there is no room whatsoever and under any circumstances to justify torture 130. If a State is informed or has reasonable grounds to suspect that any persons are held incomunicado at foreign military bases on its territory, despite its limited jurisdiction over foreign military bases, its responsibility under the European Convention on Human Rights is still engaged, unless it takes all measures which are within its power in order for this irregular situation to end. 131. As a rule, a State cannot search foreign military bases on its territory unless this is allowed under the relevant treaties or unless the host State is authorised by the sending State to do so. However, the right to detain non-military personnel does not fall under the ordinary rights and powers that are connected directly with the establishment and operation of the sites at which the foreign forces and installations are located (see para. 106 above), unless the site falls under the jurisdiction of the sending State under the applicable SOFA, such as the NATO-SOFA (see footnote 68 above). 132. The host State is therefore entitled and even obliged to prevent, and react to such abuse of its territory. It could exercise its powers in respect of registration and control of aliens, and demand identification and movement orders of those present on the military base in question. Access to such military bases, assuming that it had been freely granted under the military base agreement, would require notification under normal conditions. In addition, appropriate diplomatic channels can be used in order to protest against such practice. 83 European Court of Human Rights, Chahal v. United Kingdom judgment of 15 November 1996.