Iraq's prime minister has declared the 'end of Daesh' after capturing an ISIS stronghold
Haider Al-Abadi made the announcement hours after the al-Nuri Mosque came back under government.
The mosque is now a ruin after ISIS forces destroyed it last week, but possesses huge symbolic value.
It is the site where ISIS leader Abu Bakr al-Baghdad declared a new caliphate in 2014, announcing its intention to capture ever-greater swathes of territory.
But after eight months of grinding urban warfare, ISIS have been all but forced out of Mosul, formerly their biggest power base outside of Raqqa in Syria.
Al-Abadi tweeted a celebration of the victory, in which he said the world is seeing "the end of the fake Daesh state", and pledged to hunt down all of its remaining fighters.
Earlier on Thursday, the Iraqi military said that they expect to have completely retaken Mosul in the next few days.
It came as new analysis of ISIS's power base found that it has lost 60% of its power base and 80% of its revenue since its peal in January 2015.
The cost of the battle has been enormous, however. In addition to military casualties, thousands of civilians are estimated to have been killed.
About 900,000 people, nearly half the prewar population of the northern city, have fled the battle, mostly taking refuge in camps or with relatives and friends, according to aid groups.
Those trapped in the city suffered hunger and deprivation as well as death or injury, and many buildings have been ruined.
Arduous task
Counter Terrorism Service troops captured al-Nuri Mosque's ground in a "lightning operation" on Thursday, a commander of the US-trained elite units told state TV.
Civilians living nearby were evacuated in the past days through corridors, he added.
CTS units are now in control of the mosque area and the Hadba and Sirjkhana neighborhoods, and they are still advancing, a military statement said.
A US-led international coalition is providing air and ground support to the Iraqi forces fighting through the Old City's maze of narrow alleyways.
But the advance remains an arduous task as the insurgents are dug in the middle of civilians, using mortar fire, snipers, booby traps, and suicide bombers to defend their last redoubt.
The military estimated up to 350 militants were still in the Old City last week but many have been killed since.
They are besieged in 0.4 square mile, making up less than 40% of the Old City and less than 1% of the total area of Mosul, the largest urban center over which they held sway in both Iraq and Syria.
Those residents who have escaped the Old City say many of the civilians trapped behind Islamic State lines - put last week at 50,000 by the Iraqi military - are in a desperate situation with little food, water, or medicine.
Abu Bakr al-Baghdadi proclaimed himself "caliph," or ruler of all Muslims, from the Grand al-Nuri Mosque's pulpit on July 4, 2014, after the insurgents overran vast swathes of Iraq and Syria.
His speech from the mosque was the first time he revealed himself to the world, and the footage broadcast then remains the only video recording of him as "caliph."
He has left the fighting in Mosul to local commanders and is believed to be hiding in the border area between Iraq and Syria, according to US and Iraqi military sources.
The Islamic State last week broadcast a video showing much of the mosque and brickwork minaret reduced to rubble. Only the stump of the Hunchback remained, along with a dome of the mosque supported by a few pillars that resisted the blast.
The mosque was named after Nuruddin al‑Zanki, a noble who fought the early Crusaders from a fiefdom that covered territory in modern-day Turkey, Syria, and Iraq. It was built in 1172-73, shortly before his death, and housed an Islamic school.
The Old City's stone buildings date mostly from the medieval period. They include market stalls, a few mosques and churches, and small houses built and rebuilt on top of one another over the ages.