Militants assaulted a prison in the Iraqi city of Tikrit on Thursday night, battling guards, police officers and witnesses said.
"A suicide bomber targeted the gate of the prison with a car bomb and gunmen then assaulted the prison, after which they killed the guards," a police lieutenant colonel said of the incident in the ancestral home of now-executed dictator Saddam Hussein, 160 kilometres (100 miles) north of Baghdad.
A police colonel said there were "clashes between police and gunmen inside the prison, and a curfew has been announced in Tikrit."
Another colonel said that riots broke out inside the prison after which police sought to bring them under control.
"The prisoners killed one policeman and wounded (prison director) Brigadier General Laith al-Sagmani," the colonel said, adding that "the gunmen took control of the prison, and clashes are continuing."
Witnesses said the prisoners were able to seize the guards' weapons, and that more than 100 of them escaped and were fighting security forces in the surrounding area.
The attack was reminiscent of two that took place in July and August.
Gunmen attempted to use bombs to breach a prison gate in Taji, north of Baghdad, on August 1. They employed similar tactics on the anti-terrorism directorate in the capital the day before, which the interior ministry said was an attempt to free inmates.
Al-Qaeda's front group the Islamic State of Iraq said in July that it was launching a "new military campaign aimed at recovering territory."
An earlier message posted on jihadist forums said the ISI would begin targeting judges and prosecutors, and try to help its prisoners break out of jails.