Islamic Stateinfo-icon jihadis have blown up the landmark Great Mosque of al-Nuri and its famous leaning minaret in Mosulinfo-icon, Iraqinfo-icon's armyinfo-icon said on Wednesday night.

The Iraqi army had launched a push, backed by British and American forces, to regain the medieval mosque and surrounding areas from Islamic State of Iraq and the Levant (ISIL) fighters earlier in the day.

The twelfth-century mosque, along with its minaret, was one of Iraq's most famous buildings.  

And it was where Abu Bakr al-Baghdadi, the Isil leader, declared the creation of the so-called caliphate in a speech in summer 2014 after his fighters swept through large parts of Syriainfo-icon and Iraq. 

"Our forces were advancing toward their targets deep in the Old City and when they got to within 50 yards of the Nuri mosque, Daesh (Isil) committed another historical crime by blowing up the

Nuri mosque," Staff Lieutenant General Abdulamir Yarallah, the overall commander of the Mosul offensive, said in a statement.

Haider al-Abadi, Iraq's prime minister, said the destruction of the sites was "an official declaration of defeat" by Isil in the eight-month-old battle for Mosul.

Isil later issued a statement via its Amaq propaganda agency that blamed a US air strike for the destruction of the mosque. A coalition spokesman said there were no air strikes in the area at the time.Major General Joseph Martin, who leads the US-led coalition's combined joint forces land component said the historic building's destruction was "a crime against the people of Mosul and all of Iraq and is an example of why this brutal organisation must be annihilated".

The black flag of Isil had been flying over the leaning minaret since June 2014.

The fight to retake Mosul, which has been a key Isil stronghold, was launched more than eight months ago and has displaced more than 850,000 people.On Wednesday morning, US and British-backed Iraqi forces began a push towards the mosque, having encircled jihadi fighters in the Old City.

An estimated 100,000 civilians are holed up in the Old City with the last remaining Isil troops in Mosul, the UN has stated, warning they could be used as human shields.As Iraq's Counter Terrorism Service (CTS) troops closed in on the mosque, Isil blew it up.

Iraqi officials had privately expressed the hope that the mosque could be captured in time for Eid al-Fitr, the festival marking the end of Ramadan, the Musliminfo-icon fasting month, Reuters reports. The first day of Eid falls this year on June 25 or 26 in Iraq.

Baghdadi is believed to be hiding in the border area between Iraq and Syria. Russiainfo-icon claimed last week he had been killed in an air strike, but there has been no confirmation.

Major General Rupert Jones, the British deputy commander of the international coalition fighting Isil, said: "If you were a Daesh fighter (..) I don't sense you would feel as though you are being led by Baghdadi."

The mosque was built by the Turkic ruler of Mosul, Nur al-Din Mahmoud Zangi, who helped unify Arab forces against the European Crusaders.He ordered its construction in 1172, two years before his death. The mosque and minaret are pictured on Iraq's 10,000 dinar bank note.

Originally standing at 150 feet, the minaret was leaning noticeably by the 14th century and given the nickname "al-Hadba" (the humpback). It was also sometimes referred to as Iraq's Tower of Pisa.

"The minaret of Al-Hadba has been here forever, it is part of the historyinfo-icon of Mosul, it is the symbol of the city," Ahmed Thilij Hamed, a 49-year-old resident of a neighbourhood near the Old City, told AFP on Monday.

Isil attempted to destroy the minaret in July 2014, saying the structure contradicted their fundamentalist interpretation of Islam. However, Mosul residents protected it by forming a human chain.It is the latest historically significant site in the region to be destroyed by Isil.

In May 2015, jihadists overran the oasis city of Palmyra in Syria and destroyed countless priceless artifacts.

In January, the militants blew up the famous Tetrapylon monument and damaged a Roman theatre in Palmyra.