The jail, which housed some 300 inmates, was assaulted by gunmen driving police vehicles after a car bomb exploded outside the main gate late yesterday, security sources said. Twelve prison guards and seven gunmen were killed in clashes.

Security forces managed to regain control of the jail, in the city of Tikrit, early on Friday, but an official said more than 50 prisoners were still on the run, among them leading members of al Qaeda who had been sentenced to death on more than ten counts.

"There was clear negligence and laxness by those who are in charge of this prison. The operation was pre-planned, well prepared," Hakim Al-Zamili, a member of parliament's security and defense committee, told reporters.

A curfew was imposed and helicopters hovered over the city, the home town of the executed former President Saddam Hussein.

Around 20 escapees were recaptured overnight, but Zamili said it would be tough to track down the rest because they had destroyed prison records before fleeing.

"All documents, files, pictures and all identifications of those prisoners were burned. I think the security forces will find it very difficult to identify those who escaped."

Violence in Iraq has eased since its height in 2006-2007 when sectarian slaughter killed thousands. But Sunni Islamists and an al Qaeda affiliate still launch regular attacks, seeking to destabilize the country and undermine its Shi'ite-led government.

Prison breaks are not uncommon. Last September, 35 prisoners facing terrorism charges escaped via a sewage pipe from a temporary jail in the city of Mosul, an al Qaeda stronghold.