Iraqi troops staged on Sunday an offensive against ISIS positions south of Mosul, which is the largest city under militant control.

The step came as the U.S.-led coalition intensified its campaign against the militants on multiple fronts across their self-proclaimed caliphate.

Officers involved in the operation said Iraqi forces had advanced in tanks and armored vehicles towards the village of Haj Ali, about 60 km (40 miles) south of Mosul, under cover of coalition airstrikes and artillery fire.

Iraqi forces are also advancing on the edge of the ISIS bastion of Fallujah further south, while in Syria U.S.-backed forces are encircling the militant-held town of Manbij.

Iraqi troops were deployed to the northern Makhmour area earlier this year and launched an operation in March touting it as the beginning of a bigger campaign to retake Mosul. Since then, Iraqi forces have captured a handful of villages on the eastern bank of the river Tigris.

The commander of the operation blamed the slow pace on a lack of tanks and said he did not have enough men to hold ground after it was retaken from the militants.

ISIS had been weakened financially by the loss of many of its oil wells and was struggling to sell oil because its convoys have been targeted by U.S.-led international coalition forces in Iraq and Syria.

Last week, an armored brigade was deployed to Makhmour, along with boats and bridges to enable troops to cross the Tigris river to the ISIS hub of Qayara on its western bank.

Qayara is home to an airfield that will serve as a pivotal staging ground for the future operation to recapture Mosul, and control of the oil town would also isolate territory the militants control further south and east.