Several inmates seized a cache of grenades and other weapons and killed six security officers, including a high-ranking counterterrorism official. The inmates overran part of the prison until they were beaten back by an Iraqi police assault team around 4:30 a.m. Eleven inmates were killed, the officials said.
It was the latest in a string of riots and jailbreaks that have embarrassed government officials and exposed gaping security flaws in Iraq’s detention system.
“These terrorists took the benefit of carelessness,” said Hakim al-Zamili, who sits on the Iraqi Parliament’s security committee and is a vocal critic of the government. “The Iraqis are using the wrong strategy with prisoners and terrorists.”
Iraqi officials said that the assault appeared to have been planned in advance, but they provided few details.
The office of the prime minister, Nuri Kamal al-Maliki, released a statement saying that he had formed a committee to investigate the episode.
He ordered security forces to be “more alert” to prevent future breaches.
The violence came amid warnings of heightened attacks in revenge for last week’s killing of Osama bin Laden in Pakistan. Iraqi intelligence officials said that the inmates were members of the Sunni extremist group Al Qaeda in Mesopotamia, and that the authorities had been interrogating them about possible reprisals for Bin Laden’s death.
On Thursday, a suicide bomber attacked a police training center in the southern Shiite city of Hilla, killing 25 people. The authorities blamed Al Qaeda in Mesopotamia for the assault.
The melee inside the Baghdad prison began around 10 p.m. on Saturday when the man believed to have masterminded the church attack, Huthaifa al-Batawi, seized a police lieutenant’s pistol, shot him in the head and led other inmates on a rampage, the officials said.
It was unclear exactly where Mr. Batawi was when he grabbed the gun, but the authorities said that he and the other inmates had not been handcuffed, making it easier for them to overpower their captors, break out of a holding area and overrun the jail.
They killed five other officers, including Brig. Gen. Moayed al-Saleh, who oversaw counterterrorism operations in Karada, an upper-middle-class neighborhood of Baghdad.
As reinforcements arrived, five inmates were killed trying to escape in a stolen police vehicle, and five others were killed later by the Iraqi police.
The assault was especially galling because it occurred in the shadow of the heavily guarded headquarters of Iraq’s Interior Ministry and happened in a prison that holds dozens of high-value detainees.
Iraqi politicians were quick to criticize security measures in the facility, where the grenades seized by the inmates had been sitting on a table.
Critics said that officers there appeared to underestimate the threat posed by the inmates.
“They are very dangerous, these prisoners,” said Adnan al-Asadi, a former deputy interior minister and a member of Parliament.
Security officials said that of the roughly 220 inmates, 38 were said to have been involved in the Oct. 31 assault on Our Lady of Salvation Church.
That attack, the worst against Iraqi Christians since the American invasion, left more than 50 people dead.
The violence and uncertainty it wrought helped drive more of the country’s dwindling population of Christians to seek safety in the north, or leave Iraq entirely.
?Mr. Maliki and other top officials promised to hunt down terrorists after the church siege, and in late November, the Interior Ministry announced Mr. Batawi’s arrest with pride, saying that he had been captured after “long hard efforts.”
Duraid Adnan and Khalid D. Ali contributed reporting.
