The official, who declined to be identified, said the incident took place as government forces closed in on Islamic State fighters in the Old City and other districts, in an offensive intended to crush the hardline group in what was once the de facto capital of their self-proclaimed Islamic caliphate.
A media officer for the Interior Ministry's Rapid Response units, Lieutenant Colonel Abdel Amir al-Mohammedawi, denied that any police officers had been captured when asked for comment.
But the Interior Ministry official told Reuters the nine men were seized in the early hours of Monday in the Bab Jadid district.
Federal police sources later said the officers had been killed and Iraqi forces were trying to recover the bodies.
Islamic State has a record of torturing and mutilating captives - civilian and military - so the incident will weigh heavily of the minds of the government troops in the street-by-street fighting for western Mosul, now in its second month.
In the capital, Baghdad, a car bomb killed at least 23 people and wounded more than 45 in a mainly Shi'ite southern district, police and medical sources said.Read more at Reuters