Iraqi forces storm ISIS-held Old City of Mosul

Iraqi forces beganstorming the ISIS-held Old City of Mosul on Sunday anassault they hope will be the last in the eight-month campaignto seize the militants' stronghold.

The historic district is the last still under control of themilitants in the city, which used to be their de facto capital in Iraq.

It is a densely populated maze of narrow alleyways wherefighting is often conducted house by house.

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About 100,000 civilians remain trapped there in harrowingconditions, with little food, water and medicine and limitedaccess to hospitals, according to the United Nations.

"This will be a terrifying time for around 100,000 peoplestill trapped in Mosul's Old City ... now at risk of gettingcaught up in the fierce street-fighting to come," theInternational Rescue Committee (IRC) said in a statement.

"This is the final chapter" in the offensive to take Mosul,said Lt.-Gen. Abdul Ghani al-Assadi, commander of theCounter Terrorism Service (CTS) elite units spearheading theassault.

A U.S.-led international coalition is providing air andground support to the campaign.

Airstrikes, armoured vehicles

Several airstrikes during the day hit a medical complexlocated just north of the Old City, alongside the western bankof the Tigris River, a Reuters TV reporter said.

Armoured vehicles were heading toward the frontline north ofthe Old City as shelling and gunfire could be heard.

The medical complex, housing the two biggest hospitals ofMosul, is still held in part by the militants who are using itsbuildings as sniper outposts.

Kanaan Jiyad Abdullah aka Abu Amna ISIS's security services chief in the Old City was killed in the morningclashes, Hisham al-Hashimi, who advises several Middle Eastgovernments, told Reuters.

The Iraqi government initially hoped to take Mosul by theend of 2016, but the campaign took longer as militants dug into the middle of civilian communities to fight back.

ISIS is also using suicide car and motorbike bombs,booby traps and sniper and mortar fire against the troops.

"The buildings of the old town are particularly vulnerableto collapse even if they aren't directly targeted, which couldlead to even more civilian deaths than the hundreds killed sofar in airstrikes across the rest of the city," the IRC said.

"We are trying to be very careful, using only light andmedium weapons ... to avoid casualties among civilians," CTScommander Major General Maan Saadi told Iraqi state TV.

Trapped civilians become casualties

Hundreds of civilians were killed near the frontlines in thepast three weeks while fleeing the Old City, as Iraqi forcescouldn't fully secure exit corridors.

"We expect thousands of families to escape from the OldCity; we made all preparations to evacuate them from thefrontlines," army colonel Salam Faraj told Reuters.

ISIS snipers are shooting at families trying toflee on foot or by boat across the Tigris River, as part of atactic to keep civilians as human shields, the UNsaid onFriday.

Number of ISIS fighters has decreased

The Iraqi army thinks the number ofISIS fightersin the Old City doesn't exceed 300, down from nearly 6,000 whenthe battle of Mosul started on Oct. 17.

"The operation now is about street fighting, air andartillery strikes will be limited because the area is heavilypopulated and the buildings fragile," CTS spokesman Sabahal-Numan told al-Hadath TV in Dubai.

Iraqi government forces regained eastern Mosul in January,then a month later began the offensive on the side located westof the Tigris, which includes the Old City.

The fall of Mosul would, in effect, mark the end of theIraqi half of the "caliphate" that ISIS leader Abu Bakral-Baghdadi declared in a speech from an historic mosque in theOld City three years ago, covering parts of Iraq and Syria.

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The group is also retreating in Syria, mainly in the face ofa U.S.-backed, Kurdish-led coalition. Its capital there, Raqqa,is being besieged.

Baghdadi has left the fighting in Mosul and Raqqa to fieldcommanders, to become effectively a fugitive focused on his ownsurvival in the border area between Iraq and Syria.

U.S. airstrikes have killed several commanders of the groupover the past two years, including Abu Omar al-Shishani, a topmilitary commander, chief propagandist Abu Mohammed al-Adani,and Abu Ali al-Anbari, the former top civilian administrator.

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About 200,000 people were estimated to be trapped behindISIS lines in Mosul in May, but the number has declinedas government forces have thrust further into the city.

About 850,000 people, more than a third of the pre-warpopulation of the northern Iraqi city, have fled, seeking refugewith friends and relatives or in camps, according to aid groups.