(Edits, adds more details, quote)
By Ziad al-Sinjary
MOSUL, Iraq, June 6 (Reuters) - Dozens of people including civilians were killed on Friday in fighting between Sunni Islamist insurgents and Iraqi government troops in the northern city of Mosul, a day after a curfew was imposed there.
The fighting erupted in Mosul a day after government forces used helicopters to bomb militants and retake control of the city of Samarra further to the south.
The insurgents have been gathering momentum over the past year in their conflict with Iraq's Shi'ite Muslim-led government, particularly in western provinces bordering Syria such as Nineveh, of which Mosul is the capital.
Security sources said the militants 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 Muwaffakiya near Mosul, two suicide car bombs exploded on Friday, killing six members of the Shabak minority that lives there and is often a target for Sunni Islamist insurgents.
Mohammed Ibrahim, a member of the security and defence committee in the provincial council of Nineveh, said the army had killed 105 militants and destroyed 20 of their vehicles mounted with machine guns, preventing them from holding ground.
It was not possible to confirm the death toll estimates.
By Friday evening, 90 percent of Mosul was back under government control, security sources said, and the army was still firing mortar rounds at remaining pockets of resistance.
Most of the militants withdrew into the desert, made their way to neighbouring provinces or simply took cover among the local population.
Mosul has long been a stronghold for insurgents, who have been invigorated by the conflict in nearby Syria. The Sunni militant Islamic State in Iraq and the Levant (ISIL) is active on both sides of the border.
To the south of Nineveh lies the Sunni-dominated province of Anbar, where the army has been fighting tribal and Islamist groups including ISIL since they overran two cities early this year.
"What the western areas of the city (Mosul) witnessed today is a scheme by ISIL to disperse the security effort and alleviate the pressure on the terrorists in Anbar province," Ibrahim said.
Also on Friday, security forces thwarted an attempt by militants to seize the headquarters of the counter-terrorism police in the centre of Baquba in Diyala province. Two people were killed in the clashes, the chief of police and medics said.
Bloodshed in Iraq remains below levels seen in 2006 and 2007 when sectarian Shi'ite-Sunni killings reached their peak, but last year was Iraq's deadliest since violence began to ease in 2008. Nearly 800 people were killed across Iraqi in May alone, making it the bloodiest month so far this year.
On Thursday, the militants came within striking distance of the Shi'ites' Askari shrine, whose destruction in 2006 unleashed the worst bout of Sunni-Shi'ite violence since the U.S.-led invasion of Iraq in 2003. (Additional reporting by Isra al-Rubei'i and Raheem Salman; Writing by Isabel Coles; Editing by Gareth Jones)