Iraqi armed forces launched an operation on Saturday to capture one of the few last Daesh-held enclaves in Mosul, according to the military.
Multiple security forces are attacking "what remains of the unliberated areas" on the west bank of the River Tigris, the Joint Operations Command said in a statement.
"Army forces attacked Al-Shifaa neighbourhood and the Republican Hospital, federal police forces Al-Zinjili neighbourhood, and Counter-Terrorism forces attacked Al-Saha al-Oula neighbourhood," it added.
The fall of the city would effectively mark the end of Iraqi half of the "caliphate" declared nearly three years ago by Daesh leader Abu Bakr al-Baghdadi, which also covers parts of Syria.
The Iraqi air force dropped leaflets on Friday urging residents in the enclave to flee, although humanitarian groups fear for the safety of civilians trying to escape.
Desperate civilians trapped behind Daesh lines now face a harrowing situation with little food and water, no electricity and limited access to hospitals.
The United Nations expressed "deep concern" for the hundreds of thousands of civilians trapped behind Daesh lines, in a statement on Saturday from the organisation's under-secretary-general for humanitarian affairs, Stephen O'Brien.
"Although the UN is not present in the areas where fighting is occurring, we have received very disturbing reports of families being shut inside booby-trapped homes and of children being deliberately targeted by snipers," he said.
Daesh members have laid sheets of corrugated metal over pebbles in the alleys as an early warning system, residents said. The grinding noise produced by treading on it would alert them to any troop movements or civilians trying to escape.
The United Nations last week said up to 200,000 more people could flee Mosul as fighting moves to the Old City.
About 700,000 people, about a third of the pre-war city's population, have already fled, seeking refuge either with friends and relatives or in camps.
Iraqi forces launched a major operation to retake Mosul in October 2016, fighting their way to the city and retaking its eastern side before setting their sights on its smaller but more densely populated west.