The rights group, Amnesty International, says women and children are being sexually abused in two prisons in north-eastern Nigeria.
It says the abuse is being carried out by inmates and prison warders.
A former convict and prison warden told the rights group that the abuse of children by other inmates was widespread in the prison.
Three former female detainees also claimed at least 15 of their peers were victims of rape, with soldiers demanding sex in exchange for basic necessities and the promise of freedom.
A spokesperson for the governor of north-eastern Borno state told the BBC that an investigation by a committee, set up specifically to deal with these allegations, was ongoing, and that its findings would be published in due course.
Thousands of people are being held in the jails in northern Nigeria, many suspected to have links with the Islamist group, Boko Haram.