US troops in Afghanistan have been accused of \"systemic\" abuse of prisoners by a human rights group. Human Rights Watch (HRW) said it had documented \"numerous cases of mistreatment of detainees,\" similar to those reported in Iraq. The group said it had repeatedly warned Washington about the problems. The United Nations has meanwhile warned that trust in US forces in Afghanistan is at risk if the allegations are not properly investigated and made public. HRW say the deprivations suffered by prisoners include sleep deprivation, exposure to freezing temperatures, severe beatings, and detainees being stripped and photographed naked. The charges come a day after the US announced it was investigating allegations of abuse by an Afghan police officer who was detained in 2003. Former police colonel, Sayed Nabi Siddiqui, 47, was quoted by the New York Times as saying he was subjected to sexual abuse, taunting and lack of sleep while being held at a US base in Gardez, east of the capital Kabul. Mr Siddiqui told the newspaper he was wrongly detained on 15 July after reporting police corruption. In March, a HRW report said the US detention system in Afghanistan violated international law. It said the US military had still to \"explain adequately\" the deaths of three detainees in American custody. Two deaths at Bagram airbase were ruled as homicides by US military doctors. The group is now calling for the immediate release of details regarding these deaths. \"It\'s time now for the United States to publicise the results of its investigations of abuse, fully prosecute those responsible, and provide access to independent monitors,\" HRW\'s Afghan researcher, John Sifton, said. UN spokesman Manoel de Almeida de Silva said that he had been receiving reports of violations for the past two years. \"More than once we have requested details of investigations into the deaths of two detainees at Bagram,\" he said, \"but regrettably we have not yet had access to this.\" Both the UN and HRW have backed calls by Afghan human rights organisations for access to carry out checks on detainees in US custody. At least 300 people, the majority of them Afghans, are believed to be held at the main US base at Bagram, north of Kabul, and an unknown number at other sites. (BBC)