Iraqi security officials say more than 100 Islamic State (IS) militants launched a counterattack in Mosul, killing six Federal Police and three civilians in clashes that were still underway.
An army officer and a police officer say the militants sneaked into the western Dandan neighbourhood at dawn Wednesday and took over a mosque, where they used loudspeakers to announce the assault before it was bombed from the air.
The officials spoke on condition of anonymity as they were not authorised to release information.
US-backed Iraqi forces have been battling the extremists in Mosul, the country's second-largest city, since October.
The militants are now largely confined to a few neighbourhoods.