Displaced Iraqis flee their homes as Iraqi forces battle with ISIS, in western Mosul, Iraq March 24, 2017.

Iraqi forces launched a renewed attack against militants in Mosul’s Old City on Monday, a senior commander said.

The United Nations has warned that 400,000 people are “trapped” in the central Mosul area under siege-like conditions, as Iraqi forces battle ISIS for the city’s west.

“Federal Police and Rapid Response Division units began to advance today on the southwestern axis of the Old City,” Lieutenant General Raed Shakir Jawdat, the commander of the federal police, said in a statement.

Jawdat said that one of their targets is Faruq Street, which runs near the Al-Nuri mosque.

ISIS Chief Abu Bakr al-Baghdadi made his only known public appearance at the mosque after ISIS seized Mosul in 2014, calling on Muslims to obey him.

Iraqi forces have been operating in the area of the Old City for several weeks, but they have faced tough resistance and progress in the area has been slow.

ISIS overran large areas north and west of Baghdad in 2014, but Iraqi forces have since retaken much of the territory they lost.

Iraqi forces launched the operation to retake Mosul, the country’s second city, in October, retaking its eastern side before setting their sights on its smaller but more densely-populated west.