IS fighters have blown up al Nouri mosque in Mosul, where the group's leader declared the caliphate, the Iraqi military has said.
The Ministry of Defence said the group destroyed the mosque and iconic leaning minaret when fighters detonated explosives inside the structures.
A statement from the commander of the Mosul offensive, Staff Lieutenant General Abdulamir Yarallah, said the explosion took place as Iraqi forces, which have been advancing in the Old City, had gotten within 50 metres of the mosque.
"The Daesh (Islamic State) terror gangs committed another historical crime by blowing up the al Nouri mosque and its historical al-Hadba minaret," the statement said.
The medieval mosque, also known as Mosul's Great Mosque, is where IS leader Abu Bakr al Baghdadi declared a so-called Islamic caliphate in 2014. It was seen as a key symbolic prize in the fight for Mosul.
The minaret stood for more than 840 years.
IS blamed a US strike for the mosque's destruction.
Iraqi forces this week launched a push into Mosul's Old City, where the last IS fighters are holed up with an estimated 100,000 civilians, according to the UN.
The fight to retake Mosul was launched more than eight months ago and has displaced some 850,000 people.
