Iraqi soldiers fire a mortar toward Islamic State militants on the outskirts of Fallujah, west of Baghdad, April 20, 2016. REUTERS/Stringer/Files

Iraqi forces clashed with Islamic State militants near Falluja on Monday while bombing central districts in the early hours of an offensive to retake the militant stronghold just West of Baghdad that could last several weeks.

A resident said “that some of the first direct engagement occurred in al-Hayakil area on the city’s southern outskirts”. Troops also approached the northern suburb of Garma, the top municipal official there said, to clear out militants before turning attention towards the city centre.

Air strikes and mortars overnight targeted neighbourhoods inside the city proper where Islamic State is thought to maintain its headquarters. But the bombardment had eased by daylight.

Iraqi military spokesman Brigadier General Yahya Rasool, speaking on state television, described the forces advance as “careful” and reliant on engineers to dismantle roadside bombs planted by the militants.

Iraqi forces have surrounded the city since last year but focused most combat operations on IS-held territories further west and north.

The authorities have pledged to retake Mosul this year in keeping with a U.S. plan to dislodge Islamic State from their de facto capitals in Iraq and Syria.

But the Falluja operation, which is not considered a military prerequisite for advancing on Mosul, could push back that timeline.

Two offensives by U.S. forces against al Qaeda insurgents in Falluja in 2004, has left the city badly damaged, each lasted about a month

Reuters/Omolayo Alabi