Hundreds of convicts, including senior members of al Qaeda, broke out of Iraq's Abu Ghraib jail as comrades launched a military-style assault to free them, authorities said on Monday.
The deadly raid on the high-security jail happened as Sunni Muslim militants are re-gaining momentum in their insurgency against the Shi'ite-led government that came to power after the U.S. invasion to oust Saddam Hussein.
Suicide bombers drove cars packed with explosives to the gates of the prison on the outskirts of Baghdad on Sunday night and blasted their way into the compound, while gunmen attacked guards with mortars and rocket-propelled grenades.
Other militants took up positions near the main road, fighting off security reinforcements sent from Baghdad as several militants wearing suicide vests entered the prison on foot to help free the inmates.
Ten policemen and four militants were killed in the ensuing clashes, which continued until Monday morning, when military helicopters arrived, helping to regain control.
By that time, hundreds of inmates had succeeded in fleeing Abu Ghraib, the prison made notorious a decade ago by photographs showing abuse of prisoners by U.S. 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 defence committee in parliament, told Reuters.
"The security forces arrested some of them, but the rest are still free."
One security official told Reuters on condition of anonymity: "It's obviously a terrorist attack carried out by al Qaeda to free convicted terrorists with al Qaeda."
A simultaneous attack on another prison, in Taji, around 20 km (12 miles) north of Baghdad, followed a similar pattern, but guards managed to prevent any inmates escaping. Sixteen soldiers and six militants were killed.
Sunni insurgents, including the al Qaeda-affiliated Islamic State of Iraq, have been regaining strength in recent months and striking on an almost daily basis against Shi'ite Muslims and security forces amongst other targets.
The violence has raised fears of a return to full-blown conflict in a country where Kurds, Shi'ite and Sunni Muslims have yet to find a stable way of sharing power.
In the northern city of Mosul, 390 km (240 miles) north of Baghdad, a suicide bomber detonated a vehicle packed with explosives behind a military convoy in the eastern Kokchali district, killing at least 22 soldiers and three passers-by, police said.
Suicide bombings are the hallmark of al Qaeda, which has been regrouping in Mosul, Iraq's third-largest city and capital of the Sunni-dominated Nineveh province.
A separate attack in western Mosul killed four policemen, police said.
Relations between Islam's two main denominations have been put under further strain from the civil war in Syria, which has drawn in Shi'ite and Sunni fighters from Iraq and beyond to fight against each other.
Recent attacks have targeted mosques, amateur football matches, shopping areas and cafes where people gather to socialise after breaking their daily fast for the holy Muslim month of Ramadan.
Nearly 600 people have been killed in militant attacks across Iraq so far this month, according to violence monitoring group Iraq Body Count.
That is still well below the height of bloodletting in 2006-07, when the monthly death toll sometimes exceeded 3,000.