Al Qaeda said Tuesday that it was behind the prison break that freed more than 500 inmates from two Iraqi jails.
Suicide bombers drove explosive-packed cars to the Abu Ghraib and Taji jails near Baghdad on Sunday night.
At least 20 security guards died as gunman stormed the buildings and attacked guards with mortars and rocket-propelled grenades.
Hundreds of inmates — including some senior Al Qaeda members — managed to flee Abu Ghraib prison, made notorious through photos showing the abuse of prisoners at the hands of US soldiers.
"The number of escaped inmates has reached 500, 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."
The Islamic State of Iraq and the Levant, formed earlier this year through a merger of Al Qaeda's affiliates in Syria and Iraq, said it stormed the jails after months of preparation.
The attacks came exactly a year after the leader of Al Qaeda's Iraqi branch, Abu Bakr al-Baghdadi, launched a "Breaking the Walls" campaign that made freeing its imprisoned members a top priority, the group said in a statement.
Iraqi Interior Minister Wissam al-Firaiji earlier told the BBC that attackers, whom he called terrorists, had been well-armed.
"The attack against Taji jail alone was carried out by nine suicide bombers and three car bombs driven by suicide bombers," he told reporters.
"The attackers also lobbed more than 100 mortar shells," he said, adding that the inmates were "under control" again.
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Sectarian tensions across the region have been inflamed by the civil war in Syria, which has drawn in Shia and Sunni fighters from Iraq and beyond to fight against each other.
The violence has raised fears of a return to full-blown conflict in Iraq, where ethnic Kurds, Shias and Sunnis have yet to find a stable way of sharing power.
Reuters contributed to this report.