Iraqi forces backed by helicopter strikes engaged in heavy fighting with jihadists on the outskirts of the Old City on Sunday as they pressed their offensive to recapture west Mosul.
The elite Rapid Response Force and Iraqi federal police attacked the Islamic State group militants with rifles, machineguns, mortar rounds and rockets a month after the west Mosul operation began.
The joint forces were around 100 metres (yards) south of Mosul's Iron Bridge, which has been destroyed along with other bridges spanning the Tigris River that linked the city's eastern and western sides.
Helicopters hosed IS with bullets and fired volleys of rockets in strikes aided by weather that was clearer than it had been for days, AFP correspondents said.
"The aim of the battle is to go past Al-Hadidi (Iron) Bridge northwards," Brigadier General Abbas al-Juburi of the Rapid Response units told AFP.
He said the operation was complicated by the presence of hundreds of thousands of civilians believed to have stayed on under jihadist rule.
"The difficulties are the presence of families, how to avoid opening fire on families who are used as human shields" by the jihadists, Juburi said.
"It is an ancient neighbourhood with old houses. We rarely use heavy weapons" in such conditions, he said.
The battle for the densely populated Old City, with its warrens of alleyways, was always expected to be the toughest of the campaign to retake Mosul from IS.
Iraqi authorities launched the offensive to retake the city on October 17 last year, with the support of the US-led coalition that has been carrying out strikes against IS in Iraq and neighbouring Syria since 2014.
Prime Minister Haider al-Abadi left for Washington on Sunday for talks with US President Donald Trump and will also attend a ministerial meeting on Wednesday of the 68-nation coalition line-up against IS.
In January, Iraqi forces retook the eastern sector of the city before setting their sights on the west.
At the heart of the Old City lies the Al-Nuri Mosque, where IS leader Abu Bakr al-Baghdadi in July 2014 proclaimed the IS "caliphate" in jihadist-controlled territory in Iraq and Syria.
It was Baghdadi's first public appearance, and the capture of the mosque would be highly symbolic and strategic for Iraqi forces who have in recent days taken several key IS positions.
On Saturday, elite forces battled house by house in the Old City as they tried to inch towards the mosque, but were slowed by bad weather and the complicated effort of navigating the narrow streets.
"Our forces are 800 metres (yards) from the mosque," Captain Firas al-Zuwaidi, the spokesman for Rapid Response, said on Saturday.
"The fighting is street by street, house by house," he said to the sound of mortar fire from the heart of Iraq's second city.
The Rapid Response Force is backed up by federal police who have made steady gains since Friday, taking several sites including the Al-Arbiaa market and a grain silo overlooking the Old City.
Retaking Iraq's second city would be a major blow to IS following months of jihadist losses in both Iraq and Syria.
Iraqi authorities say more than 150,000 people have fled their homes in west Mosul, with two-thirds finding shelter in camps near the city.
On Saturday, father of five Samir Hamid and 33 family members displaced by the fighting returned home to the Wadi Hajar district recaptured by Iraqi forces, saying the camps were too crowded.
On Sunday, the United Nations Population Fund (UNFPA) said it has deployed "the first mobile delivery unit" inside west Mosul "to meet the lifesaving needs of primary health care for women and girls".