Geneva - Untold thousands of men, women and children are being held in horrific conditions in Libya by armed groups who subject them to torture and other abuses, a UN report said Tuesday.Fresh findings from the UN rights office and the UN Support Mission in Libya (UNSMIL) found that Libya was plagued by "widespread, prolonged arbitrary and unlawful detention and endemic human rights abuses in custody".Libya descended into chaos following the overthrow of longtime dictator Muammar Gaddafi in 2011, with dozens of armed factions filling the power vacuum. Since renewed hostilities broke out in 2014, armed groups on all sides have rounded up suspected opponents, critics, activists, medical professionals, journalists and politicians, Tuesday's report said."This report lays bare not only the appalling abuses and violations experienced by Libyans deprived of their liberty, but the sheer horror and arbitrariness of such detentions," the UN rights chief Zeid Ra'ad Al Hussein said in a statement."These violations and abuses need to stop, and those responsible for such crimes should be held fully to account." * Sign up to News24's top Africa news in your inbox: SUBSCRIBE TO THE HELLO AFRICA NEWSLETTERThe report however did not look at the widespread abusive detention of migrants in lawless Libya, which has long been a major transit hub for people from Africa and elsewhere trying to reach Europe.Burnt with cigarettes According to the report, an estimated 6 500 people were languishing in official prisons overseen by Libya's Judicial Police, under the justice ministry, as of last October. But it stressed there were no available statistics for facilities that fall under the ministries of interior and defence, nor for those run directly by armed groups.Such facilities "are notorious for endemic torture and other human rights violations or abuses," the report said. It detailed how armed groups routinely hold people incommunicado and systematically subject them to torture, including beatings with metal bars, flogging on the soles of the feet, burning with cigarettes and the use of electric shock.Women detainees are meanwhile at high risk of sexual abuse, the report warned, pointing out that "in some facilities, women detainees are forced to strip and are subjected to invasive cavity searches by male guards or under the gaze of male officials."FOLLOW News24 Africa on Twitter and FacebookIt also pointed to allegations of deaths in custody, with the bodies of hundreds of people taken and held by armed groups found in the streets, hospitals and rubbish dumps, many bearing signs of torture or gunshot wounds.The report called for the immediate release of all those detained arbitrarily in Libya, and urged the authorities to ensure that all of those lawfully detained be transferred to official prisons.It also called on the authorities to unequivocally condemn torture, ill-treatment and summary executions, and to ensure that any perpetrators of such crimes be held accountable.