An attack on the infamous Abu Ghraib prison in Iraq is reported to have set free more than 500 al-Qaida militants, while unconfirmed reports say over 1,000 have fled.
The escaped inmates include senior al-Qaida terrorists who were facing the death penalty.
Scores of militants and security personnel have also been killed in the military-style raid.
The late night attack on Sunday was orchestrated by suicide bombers and gunmen leading to an hour-long battle with the security forces.
Suicide bombers drove their explosives-filled cars ramming the gates of the prison, which is located on the outskirts of the capital Baghdad. This was swiftly followed by attacks on the prison with mortar fire and rocket-propelled grenades.
The prison can house up to 15,000 detainees. An initial probe suggests the insurgents had inside help.
"It cannot be tolerated. Those proved negligent in the prison's administration must be held accountable," Hakem al-Zamli, a member of parliament's security and defence committee told AFP.
Although some of the fleeing inmates were captured by police, many are still at large.
The raid on the prison has yet again highlighted the deteriorating security situation in Iraq.
"It's obviously a terrorist attack carried out by al-Qaida to free convicted terrorists with al-Qaida," a security official told Reuters.
The Iraqi arm of the Islamic militant group had launched a campaign dubbed as "Breaking the Walls" exactly a year ago in which freeing prisoners was the top priority.
"This big security failure shows that the top security commanders have failed to sort out any solutions for the ongoing security deterioration. The terrorists, not the security forces, are now taking the initiative," said lawmaker Shawan Mohammed Taha, according to the Associated Press.
The militants carried out a simultaneous attack on another prison in Taji, which security forces believe was for distraction as the main target of their attack was Abu Ghraib.