Tens of thousands of civilians are trapped inside the strategically vital city in central Iraq which ISIS seized two years ago.

With the operation in its second week, convoys of special forces could only inch forward on the dusty southern outskirts of the city as a handful of airstrikes sent up plumes of white smoke above clusters of low buildings on the fringes of the city's dense urban terrain.

More than 50,000 people are believed to be still inside Fallujah, and the UN estimates 20,000 of them are children, warning they face a dire humanitarian situation in addition to the risk of forced recruitment by the extremists.

Visiting the frontline, Prime Minister Haider al-Abadi admitted the pace of the offensive had slowed but he emphasized the priorities of the operation were protecting civilian lives and minimizing casualties.

Mr al-Abadi said ISIS was using civilians as human shields and he urged residents to leave via safe corridors or stay inside their homes.

'The main goal of the military operation now is to reduce civilian and army casualties,' he said.

Mr al-Abadi said his forces had made a 'remarkable advance' so far and confidently predicted Iraqi troops would take down the black standard of ISIS and 'hoist the Iraqi flag inside Fallujah in the coming few days'.

The operation to take Fallujah was launched on May 22 has involved Iraqi special forces, Shi'ite militias and US-led airstrikes.

Retaking the city 40 miles west of Baghdad would represent a huge victory for the Iraqi government because Fallujah was one of the first major urban areas to fall to ISIS in 2014, Daily Mail reported.

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