Government forces have made territorial gains in the western part of Mosul as they battle to drive Daesh Takfiri militants out of their last bastion in the country’s second largest city, a high-ranking Iraqi security commander says.

Commander of Federal Police Forces Lieutenant General Shaker Jawdat said on Sunday that security personnel had advanced 100 meters in the militant-held Old City of Mosul, only hours after they began their assault to retake the rest of Mosul, Arabic-language Mawazin news agency reported.

Jawdat added that soldiers from the Federal Police have also regained control over the civil defense buildings in the area, and are targeting Daesh defense lines with missiles.

Taking back the Old City of Mosul, a densely populated warren of narrow alleyways on the western side of Mosul, is crucial to recapturing the whole of the former Daesh stronghold in Iraq.

Those who try fleeing to government-controlled areas risk being caught in the crossfire or targeted by IS snipers, Love added.

The Old City is home to the centuries-old al-Nuri mosque, where IS leader Abu Bakr al-Baghdadi delivered a Friday sermon in 2014 as his group declared an Islamic caliphate in the areas it controlled in Syria and Iraq.

The militants have lost much of that territory over the last three years, and Mosul is their last urban bastion in Iraq.

Up to 150,000 civilians are believed to be trapped in the Old City, where the militants are using them as human shields, U.N. humanitarian coordinator Lise Grande told The Associated Press on Friday. She said conditions are “desperate,” with little food and no clean water.

“We know that ISIS moved them with them as they left… locations where the fighting was going on,” Bruno Geddo, the UN refugee agency’s representative in Iraq, told AFP of Iraqis stuck in Mosul. “These civilians are basically held as human shields in the Old City.”