At least 15 policemen and 31 Sunni Islamist militants were killed in clashes on Thursday in the northern city of Mosul, sources said, on the third day of the most widespread violence in Iraq since U.S. troops withdrew in December 2011.
Gunmen attacked Mosul, 390 km (240 miles) north of Baghdad, on Wednesday night and seized western parts of the city after using a mosque loudspeaker to rally Sunnis to join the battle.
Military sources said federal police and the army regained control after surrounding a police headquarters seized by militants, who were holding 17 hostages. The federal police chief said 31 militants had been killed in the fighting.
A source at a local morgue said they had received the bodies of nine militants and 15 policemen but others had yet to be recovered.
Troops and tanks also encircled the town of Suliaman Pek, 160 km (100 miles) north of Baghdad, awaiting the arrival of special forces to drive out militants who took control overnight. The highway between Kirkuk and Baghdad was closed.
More than 100 people have been killed in fighting since Tuesday, when troops stormed a Sunni protest camp in the town of Hawija near Kirkuk, 170 km (100 miles) north of Baghdad, triggering clashes that quickly spread to other Sunni areas in western and northern provinces.
The clashes were the bloodiest since thousands of Sunni Muslims started protests in December to demand an end to what they see as marginalisation of their sect by Shi'ite Prime Minister Nuri al-Maliki in the years following the 2003 overthrow of Saddam Hussein, a Sunni.
Sectarian violence, including bomb attacks which have killed dozens of people at a time, has increased across Iraq this year.
Provisional reports from rights group Iraq Body Count indicate about 1,365 people have been killed up to March 2013.
Militants partially blew up a pipeline carrying Iraqi crude from Kirkuk to Turkey's Mediterranean coast on Thursday, stopping the flow of oil, sources at Iraq's North Oil Company and the oil ministry told Reuters. The attack took place in the town of Shirqat, close to Hawija.
Clashes also erupted in Falluja, 50 km (32 miles) west of Baghdad, after militants attacked a federal police headquarters. The number of casualties was not known.
Sectarian bloodshed reached its height in Iraq in 2006-2007, three years into the U.S. occupation, when tens of thousands were killed.