Baghdad, Jan 8 (IANS): Islamic State (IS) militants launched a major attack on Samarra, a city in Iraq's northern central province of Salahudin, a provincial security source said.

The attack occurred at dawn when five suicide bombers blew up their explosives-laden trucks near the security checkpoints on a highway and at the western entrance of Samarra, some 120 km north of Iraq's capital Baghdad, the source told Xinhua on condition of anonymity.

The massive bombings were followed by mortar barrage on security positions inside the city while dozens of IS militants advanced in an attempt to enter the city from the western side, the source said.

Security forces opened fire on the booby-trapped trucks, which blew up just before they reached their targets, amid heavy clashes between government forces, aided by allied Shia militiamen, and the attackers, the source added.

The IS militants were forced to withdraw after government reinforcement rushed to the city from several military bases around the city, the source said.

At least seven people were killed, including five suicide bombers. Twenty-two civilians, 19 policemen and militiamen were wounded, the source added.

Large parts of the Salahudin province have been under IS control since June 11, a day after bloody clashes broke out between Iraqi security forces and the group which had controlled the country's northern city of Mosul and later seized swathes of territories in Nineveh, another northern city, and other predominantly Sunni provinces.

Late last year, Iraq's firebrand Shia cleric Moqtada al-Sadr ordered his followers to prepare for jihad, or holy war, against the IS militants to protect the holy shrines in Samarra as the IS pushed forward in northern and central parts of the country.

The predominantly Sunni city of Samarra is home to the provincial operations command of Salahudin and the Shia shrine of Imam Ali al-Hadi. The shrine contains the tombs of Ali al-Hadi and his son Hassan al-Askari, the 10th and 11th of the Shias' 12 most revered Imams.