Iraq returns to civil war? Al Qaeda group claims Abu Ghraib prison attack

Iraq in civil war; more than 250 killed in 10 days 1:46

Al Qaeda-linked militants have claimed responsibility for Monday’s assault on Iraq’s Abu Ghraib jail, which freed some of the terror network's top leaders amid U.S. fears that the country is back in civil war.

Checkpoints were set up Tuesday as the search continued for up to 500 militants freed by the attack, which followed the deaths of 250 Iraqis in 10 days of violence. 

The Islamic State of Iraq and the Levant, which was formed earlier this year through a merger between al Qaeda's affiliates in Syria and Iraq, said in a statement that it was behind the storming of the jail late on Sunday night.

The attack began when suicide bombers smashed explosives-laden cars into the prison’s front gate, while gunmen attacked guards with rocket-propelled grenades.

As fighters held off reinforcements outside, other militants, some wearing suicide vests, stormed into the prison and freed the convicts.

“Most of them were convicted senior members of al Qaeda and had received death sentences," Hakim Al-Zamili, a senior member of the security and defense committee in parliament, told Reuters.

"The security forces arrested some of them, but the rest are still free," Hakim Al-Zamili said.

The group also said it was behind a second, almost simultaneous assault on Taji Jail, to the north of city. But Iraqi authorities said those attackers had been fought off with a couple of helicopters.

They added that checkpoints had been set up around Abu Ghraib, as the search for the escapees continued.

Both attacks took place exactly a year after The Islamic State of Iraq and the Levant's most senior leader, Sheikh Abu Bakr al-Baghdadi, launched a campaign dubbed "Breaking the Walls" to make freeing imprisoned members a top priority. 

“The mujahideen brigades set off after months of preparation and planning to target two of the biggest prisons of the Safavid government," the group said in the statement, Tuesday. 

Safavid is used by hardline Sunnis as a derogatory term for Shiite Muslims and refers to the dynasty that ruled Iran from the 16th to 18th centuries.

Abu Ghraib gained notoriety because of abuses carried out by U.S. personnel while the country was under occupation following the removal of Saddam Hussein. 

The prison assaults followed a violent 10 days in the country, which has seen 250 killed by car bombs, ambushes and gun fights, according to violence monitoring group Iraq Body Count

The spiral of violence has led U.S. officials to warn that the country is sliding back into civil war, undoing the work achieved by the 'surge' of U.S. troops.

NBC News' Henry Austin and Reuters contributed to this report.