Human rights groups also accuse government of unlawfully arresting and holding hundreds of protesters and activists.
The Iraqi National Security Service has admitted to holding hundreds of people suspected of terrorism for months.
According to Human Rights Watch, the agency has been keeping them at a facility east of Mosul – which was retaken from the Islamic State of Iraq and the Levant (ISIL, also known as ISIS) group just over a year ago.
Human rights groups say abuses of detainees are commonplace in the country.
Al Jazeera’s Imran Khan has more from Baghdad.