An Iraqi army airstrike in the rebel-held northern city of Mosul has killed 60 fighters from the Islamic State group, state television has reported.

The claim could not be independently verified and the area is inaccessible to most media.

According to the report on Wednesday, which cited unnamed intelligence officials, the dawn strike targeted a central Mosul prison that was being used by Islamic State fighters as a religious court and detention facility.

The television reports said 60 fighters were killed in the strike and about 300 people who were in the group's custody were set free.

The report did not say if there were other casualties besides the Islamic State fighters and did not say who freed the prisoners or how.

The Islamic State seized Mosul, Iraq's largest second-largest city, in a blitz offensive in June that also captured large swaths of the country's north and west.

The group, which was formed from an al-Qaeda-breakaway group, have plunged Iraq into its worst crisis since the withdrawal of US troops in 2011.

The Islamic State has since imposed a self-styled caliphate in territory it controls in Iraq and Syria, imposing a harsh interpretation of Islamic law.

Iraqi government forces and allied Sunni tribal fighters have been struggling to dislodge the group from the areas they have captured, but with little apparent progress.

A Mosul resident, speaking on condition of anonymity fearing for his own safety, told the AP news agency over the phone that families of the prisoners rushed to the site to help their kin after the airstrike.

"The prison was partly damaged in the airstrike," he said, adding that he did not know if there were casualties.

Source: Agencies