Al-Qaida has said it was behind raids on two high-security prisons on the outskirts of Baghdad this week that killed dozens and set free hundreds of inmates, including some of its followers.
It said months of planning went into the highly coordinated assaults on the prisons in Abu Ghraib and Taji that began late on Sunday.
The attacks, among the most stunning in Iraq since a surge in violence began in April, have provoked sharp criticism from opponents of the government's efforts to keep the country safe. The spike in bloodshed is intensifying fears of a return to the widespread sectarian killing that pushed the country to the brink of civil war after the 2003 invasion.
In a statement, al-Qaida in Iraq dubbed the prison operation "Conquering the Tyrants," and described it as "a bold raid blessed by God" that followed a series of earlier attacks that "shook the pillars of the Safavid project" - a reference to what some Sunni Muslims see as undue Iranian influence over Iraq and its Shiite-led government.
It said the operation involved 12 car bombs, military-style barrages of rockets and missiles, suicide bombers and help from prisoners who had managed to obtain weapons on the inside.
Iraqi officials have said at least 25 members of the Iraqi security forces were killed in the attacks, along with at least 21 prisoners and 10 militants.
Iraq's Interior Ministry has said several prisoners managed to escape during the raid on Abu Ghraib, the infamous prison in Baghdad's western suburbs that was the site of well-publicised prisoner abuse at the hands of the U.S. military following the 2003 invasion.
Several Iraqi officials, including members of parliament's security and defence committee, have said more than 500 inmates escaped. Both prisons house thousands of inmates, including convicted al-Qaida militants.
Al-Qaida said the attack freed hundreds of detainees, including more than 500 mujahideen, or holy warriors.
Al-Qaida also claimed responsibility in its statement for carrying out other unspecified attacks over the past four months in response to a heavy-handed crackdown by security forces on a Sunni protest camp in the northern town of Hawija on April 23.