Gun battles and suicide bombings in and around the northern Iraqi city of Mosul have killed dozens of security personnel and civilians, according to officials and witnesses.

Friday's violence came a day after fighters launched an offensive on Samarra, also in the country’s north, killing seven members of the security forces and taking control of some areas of the city, officials said.

Security sources told Reuters news agency that fighters advanced on Mosul from the northwest and deployed in large numbers in the west of the city, killing at least four riot policemen and three soldiers in separate clashes.

In southern Mosul, five suicide bombers stormed an arms depot and some managed to detonate their vests before being 
shot, killing eleven soldiers, the sources said.

In the village of Muwafaqiya near Mosul, two suicide car bombs exploded, killing six members of the Shabak minority that lives there and is often a target for Sunni armed groups.

More attacks were reported over the course of the day, and according to Governor Atheel al-Nujaifi, clashes between fighters and security forces continued into the night.

Several armed groups are operating in Mosul but the strongest is the al-Qaeda-linked Islamic State in Iraq and the Levant.

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The assault on Samarra, a Sunni-dominated city 95km from Baghdad, started with dozens of gunmen driving into the city in SUVs and attacking security checkpoints and police stations on Thursday morning.

Reinforcements were sent in and local authorities imposed a curfew.

Helicopter gunships bombed fighters’ positions, pushing the attackers back, though they remained in control of some areas of the city by the late afternoon. Security forces said on Friday that they had regained control

Samarra was the scene of a major turning point in the Sunni-Shia sectarian struggle in Iraq following the 2003 US-led invasion. In 2006, al-Qaeda-linked Sunni fighters bombed the city's revered Shia al-Askari shrine, triggering a wave of violence that brought Iraq to the brink of civil war.

According to the United Nations, 8,868 people were killed in Iraq last year - the country's highest death toll since the peak of bloodletting in 2007.

Source: Al Jazeera and agencies