BAGHDAD — Elite Iraqi troops controlled by Prime Minister Nouri al-Maliki’s office are holding prisoners at a secret jail and torturing inmates at another facility, Human Rights Watch said Tuesday.

The Shiite-dominated security forces have faced similar allegations in the past, but the report details a pattern of abuse as recently as December despite promises of reform.

The findings raise fresh concern about the government’s treatment of detainees just six months after the U.S. military handed over full responsibility for the prison system to the Iraqis as part of its preparations to withdraw from the country by the end of this year.

Citing interviews and classified government documents, the New York-based rights group said the secret jails were under the control of the Iraqi army’s 56th Brigade and the Counterterrorism Service — both under the authority of the prime minister’s office.

“Revelations of secret jails in the heart of Baghdad completely undermine the Iraqi government’s promises to respect the rule of law,” the group’s deputy Middle East director Joe Stork said. The group also called on the Iraqis to open the facilities for inspections and visits.

Human Rights Watch quoted prisoners at a detention center called Camp Honor who described the use of torture during interrogations and cells “so crowded that we had to take turns standing and lying down.” Others said they were hung upside down for hours at a time and plastic bags were tied over their heads until they passed out.