Manfred Nowak wants to go to Uzbekistan to investigate
The UN is calling for an investigation into allegations of systematic rape and torture in Uzbekistan's justice system.
The UN Special Rapporteur on Torture, Manfred Nowak, says he has seen reports of police torture and rape.
He has called on the government to let him go to Uzbekistan to investigate. There have been previous reports that torture was routinely used in prisons.
Uzbek officials said they are investigating one case, but have made no further comment.
Mr Nowak's comments have been backed by human rights groups in Uzbekistan. They say that torture and abuse by police and investigating authorities are tacitly encouraged by senior government officials.
Families of victims say there is a culture of impunity, where police officers allegedly rape detainees without being punished.
Rayhon Soatova is in prison in Uzbekistan. Her family told the BBC that she and her two sisters were attacked by a group of drunken policemen who detained them for hooliganism last May.
They say Rayhon was gang raped by police officers while in detention. She then became pregnant and recently had a baby girl in jail.
Her older sister was also allegedly gang raped and is still in prison. The family says the youngest sister was beaten and tortured until she fainted.
She has now been released from jail, but has spent time in a mental hospital and has since been expelled from university.
The women's brother, Abdusamat, says his sisters were initially reluctant to say what really happened to them.
But then a few months later, "Rayhon described the ordeal to a police investigator. Instead of helping, he too, raped her," says Abdusamat.
"There is hope that we can prove Rayhon's case, because she became pregnant after the rape, but we cannot prove torture or the rape of my two other sisters," he adds.
In a rare move, the Uzbek authorities told the family they are investigating Rayhon's case.
The family wants a DNA test to be conducted, but officials have not responded to the demand.
Vasila Inoyatova, the director of the Uzbek Human Rights Group Ezgulik, welcomed the investigation but admitted that "we don't know if anyone will be punished as a result. It has never happened in Uzbekistan before".
Activists say police officers who violate human rights go unpunished
Ezgulik has received more than a dozen similar complaints over the past few years. Most victims decide not to go public for fear of being isolated and stigmatised in a deeply traditional society, says Ms Inoyatova.
The UN Special Rapporteur, Manfred Nowak, says that impunity is another huge problem.
"As long as people know they have nothing to fear, and that is the reality in Uzbekistan so far, it is very difficult to take effective preventive measures," he explains.
He says he is happy to investigate rape allegations by asking the Uzbek government to invite him for a fact-finding mission.
"I am ready, I also communicated that to the government repeatedly, for a follow-up mission in this particular case because I receive such conflicting information."
But so far Mr Nowak has not received an invitation.