Torture has become such an integral part of policing in Nigeria that many stations have an informal torture officer, Amnesty International says.
Both the military and police use a wide range of torture methods including beatings, nail and teeth extractions and other sexual violence, it says.
One woman accused of theft said she was sexually assaulted, and had tear gas sprayed into her vagina.
The Nigerian government has not yet responded to the rights group’s report.
Entitled Welcome to Hell Fire, it says people are often detained in large dragnet operations and tortured as punishment, to extort money or to extract “confessions” as a way to solve cases.
The use of torture is particularly extreme in the north-east in the war against Boko Haram Islamist militants, Amnesty International says.
The UK-based rights group says between 5,000 and 10,000 people have been arrested there since 2009, and executions in overcrowded detention facilities are common.
A teenage boy, pictured above, was among 50 people arrested by the army in Pokiskum in Yobe state last year on suspicion being a member of the Boko Haram.
At the time he was 15 years old and spent three weeks in custody in Damaturu and said he was beaten continuously with gun butts, batons and machetes.
He told Amnesty International that melted plastic was poured on his back and he was asked to walk and roll over broken bottles in a hole, and cold water was poured on him and others.
A former soldier who served at Damaturu confirmed that torture was routinely used at the camp.
“An electrified baton is used on a person to make them talk,” he told Amnesty International.
“People have also been tied up [outdoors] for long periods, their limbs tied to the wire around the basketball court. They tie people with their hands stretched behind their arms… people kept like that for six or seven hours lose their hands, people kept like that much longer can even die,” he said.
Amnesty International says the report was compiled using hundreds of interviews during 20 separate visits to Nigeria since 2007.