The chief of Mosul's police was killed by a car bomb on Friday and heavy clashes between insurgents and US and Iraqi forces were reported in the city, Iraq's third largest, police sources said.
Lieutenant General Jasim Muhammad Bilal and two bodyguards were killed in the blast in the ethnically diverse city, 390 km north of Baghdad.
Police also reported heavy clashes between insurgents, Iraqi and US forces after attacks on several police stations. They said nine policemen had been wounded.
In addition, Mosul authorities have ordered everyone off the streets until Saturday and closed the city's bridges across the Tigris river.
The United States recently announced that it was pulling over 3,500 troops from the USA's 172nd Stryker Brigade out of Mosul to reinforce security operations in Baghdad.