At least 10 policemen and five prisoners have been killed in clashes at a prison in the city of Tikrit, north of Baghdad.
The prison was seized by militants overnight and then retaken by police forces in fighting during which at least 81 inmates escaped.
The violence in Tikrit comes after Al-Qaeda's front group the Islamic State of Iraq (ISI) 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.
Based on reporting by dpa and AFP