Iraq’s armed forces attacked strongholds of the so-called ’Islamic State of Iraq and the Levant’ (ISIL) takfiri group north of Baghdad on Monday at the start of a campaign aimed at driving them out of the province of Salahuddin.

Iraq's armed forces attacked strongholds of the so-called 'Islamic State of Iraq and the Levant' (ISIL) takfiri group north of Baghdad on Monday at the start of a campaign aimed at driving them out of the province of Salahuddin.

The offensive is the biggest military operation in the province since the terrorists seized swaths of north Iraq last June and advanced towards the capital Baghdad.

Prime Minister Haider al-Abadi declared the start of the Salahuddin operations on Sunday during a visit to the government-held city of Samarra, where some of the thousands of troops had gathered for the offensive.

In Salahuddin, ISIL terrorists control several strongholds including Tikrit, hometown of executed former president Saddam Hussein and other Tigris river towns.

Iraq's air force was carrying out strikes in support of the advancing ground forces, who were being reinforced by troops and popular militia - known as Hashid Shaabi, or Popular Mobilisation units - from the neighboring province of Diyala to the east.

Declaring the start of operations on Sunday evening, Abadi gave ISIL supporters what he said was one last chance to lay down their arms, or face "the punishment they deserve because they stood with terrorism".