Amnesty International says Iraqi security forces use torture and other ill-treatment to extract confessions when detainees are held incommunicado.
In a new report, the London-based group says dozens of detainees have died as a result since 2004.
Amnesty says Iraq's Central Criminal Court often convicts defendants on the basis of confessions clearly obtained under torture.
Amnesty also says the defense and interior ministries are operating secret detention facilities.
It says U.S. forces had handed over tens of thousands of prisoners to Iraqi custody in 2009-2010 without any guarantees that they will be protected.
Earlier this week, Human Rights Watch urged the Iraqi government to close secret facilities or move them under control of the justice system.
Iraqi authorities have denied that there were any such secret sites.
compiled from agency reports