"Iraqi security forces are grabbing people outside of the law, without trial or known charges, and hiding them away in incommunicado sites," said Joe Stork, Human Rights Watch's deputy Middle East director.

He called on Iraqi authorities to immediately release names of all detainees and where they are being held, and to release those who have not been formally charged.

Asked for comment, Human Rights Ministry spokesman Kamil Amin said Camp Honor "was closed more than a year ago."

"All inmates were transferred to other prisons," Amin said. "We are confident that Camp Honor is not in use."

He denied that the government is running secret jails, and said all arrests and detentions follow legal standards.

The report said elite Iraqi troops controlled by Prime Minister Nouri al-Maliki are running two more secret jails in Baghdad where detainees are interrogated by judicial investigators.

The rights group also said it is withholding the identities of the people who were interviewed out of concern for their safety.