Russian security officials are regularly subjecting detainees to beatings, rape and torture, a report by Amnesty International says.
Cases of torture are said to be much more frequent in Chechnya
More than 100 cases were documented in a small number of regions, although Chechnya - where incidences are said to be much higher - was not included.
The report said in some cases convicted inmates were used to torture suspects.
The Ministry of Internal Affairs told the BBC torture did occur, but stressed that the problem was being tackled.
'Litany of horror'
Amnesty called on the Russian government to protect the rights of those in detention.
"We are hearing horrendous reports of prisoners being tortured in police detention in Russia - beatings with fists, plastic bottles full of water, books, truncheons and poles, of suffocation, the use of electroshocks and of organised rape," UK campaign director Tim Hancock said.
"It's a litany of horror and has no place in any decent justice system."
The report gave the example of Yekaterinburg, where it is alleged that at least 30 male suspects were systematically tortured in a block of the local prison between 2004 and 2006.
Convicted prisoners were allowed 24-hour access to suspects' cells, it added, saying that some victims mentioned a special room where suspects were raped.
Detainees were forced to sign confessions, which was an indication that police were coming under pressure to solve crimes, Amnesty said.
'Ploy by inmates'
The Ministry of Internal Affairs said the problem was being dealt with, by prosecuting policemen responsible.
But the authorities have also said that many torture allegations by inmates are simply a ploy to improve their custody conditions, according to the grani.ru website.
Russian law does not explicitly criminalise torture.
The Amnesty report documented 100 cases in 11 out of the country's 89 regions.
But it did not include Chechnya - where human rights groups have accused Russian and pro-Moscow Chechen security forces of widespread abuses - or other regions of the North Caucasus.
It said suspects were regularly denied access to lawyers and accused investigators of transferring suspects to inaccessible parts of the justice system, blocking access for independent monitors and preventing publication of expert reports.