From electric shocks and sexual violence to ripping out nails and teeth to extract confessions, torture has become so commonplace in Nigeria's criminal justice system that some police stations have an officer in charge of the practice, Amnesty International says.
The international rights group said on Thursday that torture was used as a matter of routine by both police and the military.
Detainees, many of them held without charge or access to lawyers, were beaten, shot, suspended upside down, starved, choked and made to sit on sharp objects, according to a new report launched in the capital Abuja.
"Many police sections in various states, including the Special Anti-Robbery Squad and Criminal Investigation Division, have 'torture chambers': special rooms where suspects are tortured while being interrogated," it said.
"Often known by different names like the 'temple' or the 'theatre', such chambers are sometimes under the charge of an officer known informally as 'O/C Torture' (Officer in Charge of Torture)."
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In the report `Welcome to hell fire' - Torture and Other Ill-treatment in Nigeria, Amnesty said they had gathered 500 claims of torture as a result of interviews conducted with victims, their families and lawyers starting in 2007.
They include the rape of female detainees as punishment or to extract a confession.
One woman described how a police officer fired tear-gas spray into her vagina after she refused to admit to an armed robbery.
Nigeria Police Force spokesman Emmanuel Ojukwu said they would study the report and investigate any abuses highlighted without impunity.
"Torture or ill-treatment is not, repeat not, an official policy of the Nigeria Police," he added.
