BAGHDAD: At least 10 Iraqi policemen and nine Sunni Islamist militants were killed in clashes on Thursday in the northern city of Mosul, the third day of the fiercest fighting since U.S. troops left Iraq in December 2011, military sources said.

Gunmen launched an attack in 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 had regained control over most of the area on Thursday but were still surrounding a police headquarters seized by militants, who were holding five hostages.

The violence, which broke out after Iraqi troops stormed a Sunni Muslim protest camp on Tuesday, deepens sectarian rifts in Iraq. More than 30 people were killed in gun battles between security forces and militants on Wednesday.

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 following the 2003 overthrow of Saddam Hussein, a Sunni.

Dozens of people have been killed in bomb attacks across the country in sectarian violence this year.