Al-Qaida-linked detainees at an Iraqi detention facility tried to overpower their guards during a prison break in a violent clash that left 17 people dead, including six police officers, officials said.
Among the detainees killed was the man accused of plotting the attack last October on a Baghdad church that left 68 people dead.
The incident at the Ministry of Interior's Baghdad compound raises questions about how a group of prisoners at what is supposed to be one of the most secure facilities in the country managed to launch such a fierce attack.
The detainees, who were accused of belonging to al-Qaida in Iraq, were being moved from a detention room to an interrogation room at the sprawling ministry compound in eastern Baghdad when one of them attacked a guard and took his weapon, said Qassim al-Moussawi, the top military spokesman in Baghdad.
Mr Al-Moussawi said the assault by the prisoners was not spontaneous but appeared to have been pre-planned. He said six police and 11 detainees were killed in the violent clash, which lasted for nearly three hours before Iraqi security forces managed to bring the situation under control.
Mr Al-Moussawi said the detainees were not shackled or restrained at the time. He said that is standard practice but that in this case, considering the fact that the detainees included prisoners accused of being involved in al-Qaida, they should have been restrained.
"I blame the security measures in this case because they were senior terrorists," he said. "Tight security measures should have been taken."
An interior ministry official on the scene said the guards violated procedure by keeping their weapons with them when moving the prisoners. Usually when prisoners are taken into the investigation room their restraints are removed but guards are not supposed to have their weapons on them at the time.
The official said about 20 to 25 prisoners were involved in the incident.
An additional eight police officers and six detainees were wounded, security and hospital officials said.