HAMDANIYAH, Iraq: The Iraqi army has been moving troops around Mosul ahead of an expected push to retake its western half from ISIS in the final decisive battle for the city, a commander said Tuesday.

"We are preparing ... to launch a big operation in order to liberate the rest of Mosul," said Brig. Walid Khalifa, deputy commander of the Iraqi Army's 9th Division.

On Tuesday afternoon, dozens of armored vehicle and troops could be seen moving around the city. Khalifa said the maneuvers began Sunday.

But even as the Iraqi forces began moving into place, ISIS launched a significant counterattack near the town of Tal Afar, west of Mosul, on Sunday night.

ISIS detonated some 17 car bombs, targeting a position held by Iraq's government-sanctioned mostly Shiite militia forces known as the Popular Mobilization Forces near Tal Afar, said Jaafar al-Hussaini, a spokesman for one of the militias.

In all, the attack lasted nine hours and killed four militiamen and 48 ISIS fighters before it was repelled al-Hussaini said.

Mosul's east was declared "fully liberated" in January – over three months since the Iraqi forces' operation to retake the city had started.

At the beginning of the operation, Iraqi forces experienced swift gains but slow and grueling urban combat followed before all of eastern Mosul was liberated. Iraqi and coalition officials are warning the fight for the west – a densely populated urban area – is likely going to be more difficult.

The United Nations has said that civilian casualty rates remain high in eastern Mosul as ISIS mortar attacks from the western side of the Tigris River – which divides the city into two – are still able to reach neighborhoods in the city's east.