Iraqi forces have battled their way along two streets that meet in the heart of Mosul's Old City, saying they aim to open routes for civilians to flee Islamic State's last stand there.
US-trained urban warfare units are leading the fight in the maze of narrow alleyways of the Old City, the last district in the hands of the Sunni Islamist insurgents.
Iraqi authorities are hoping to declare victory in the northern Iraqi city in the Muslim Eid holiday, which marks the end of the fasting month of Ramadan, during the next few days.
Military analysts say the government troops' advance will gather pace after Islamic State fighters blew up the 850-year-old al-Nuri mosque and its famous leaning minaret on Wednesday.
Its destruction gives the troops more freedom in attack as they no longer have to worry about damaging the ancient site.
It was in the al-Nuri mosque that Islamic State's leader, Abu Bakr al-Baghdadi, proclaimed its "caliphate" over parts of Iraq and Syria three years ago.
A US-led international coalition is providing air and ground support in the eight-month-old offensive to drive the militants from their de facto capital in Iraq.
A map published by the Iraqi forces media office showed the elite Counter Terrorism Service pushing along al-Faruq Street, from north to south, and Nineveh Street, from east to west.
The two roads cross in the centre of the Old City. When the troops reach this point, they will have isolated the remaining IS fighters in four separate pockets.
"The aim is to open ways for civilians to evacuate, we give them indications by lousdspeaker when it's possible," an Iraqi military spokesman told Reuters by phone.
More than 100,000 civilians, of whom half are children, are trapped in the crumbling old houses of the district, with little food, water or medical treatment.
Aid organisations say Islamic State has stopped many from leaving, using them as human shields. Hundreds of civilians fleeing the Old City have been killed in the past three weeks.
The Iraqi government once hoped to take Mosul by the end of 2016, but the bloody campaign has dragged on as the militants reinforced positions in civilian areas, launched suicide car and motorbike bombs, laid booby traps and kept up barrages of sniper and mortar fire.
The fall of Mosul would mark the end of the Iraqi half of the militants' "caliphate" as a state structure, but Islamic State would remain in control of large areas of both Iraq and Syria.
Baghdadi has left the fighting in Mosul to local commanders and has been assumed to be hiding in the Iraqi-Syrian border area. There has been no confirmation of Russian reports over the past week that he has been killed.
In Syria, the insurgents' "capital", Raqqa, is nearly encircled by a US-backed Kurdish-led coalition.