The famed 12th century mosque and minaret, dubbed Al-Hadba or "the hunchback," hosted Abu Bakr al-Baghdadi's only public appearance as IS chief, when he declared a self-styled "caliphate" after the jihadists swept into Mosul in 2014.

The structures were ravaged three years later in the final, most brutal stages of the months-long fight to rid Iraq's second city of IS.

On Sunday, dozens of government officials, religious figures, United Nations representatives and European ambassadors gathered in the large square in front of the battered mosque to see the foundation laid.

Abu Bakr Kenaan, the head of Sunni Muslim endowments in Nineveh province, set down the stone in a simple ceremony.

It bore a black Arabic inscription: "This cornerstone for the rebuilding and restoration of the Al-Hadba minaret and the Great Al-Nuri Mosque was laid on December 16, 2018."

More than a year after IS lost control of Mosul, the iconic mosque still lies in ruins. The stone gate leading up to its courtyard and the greenish dome now covered in graffiti are virtually the only parts still erect.

All that is left of the minaret is part of its rectangular base, the rest of it sheared off by fighting.

Kenaan told AFP remnants of the minaret would be preserved, while other parts of the mosque would be built afresh, along with a museum about its history and adjacent homes.

The five-year project will be financed by a $50.4 million (44.6 million euro) donation from the United Arab Emirates.

The first year will focus on documenting and clearing the site, while the next four years will see the physical restoration, the UN's heritage agency UNESCO has said.

The mosque's destruction "was a moment of horror and despair," said UNESCO Iraq representative Louise Haxthausen.

"Today as we lay the foundation stone of the Nuri mosque, we are starting a journey of physical reconstruction," she told those gathered.

The mosque takes its name from Nureddin al-Zinki, who ordered it built in 1172 after unifying Syria and parts of northern Iraq.

Its cylindrical minaret, which featured several levels of ornamental brickwork capped by a small white dome, started listing centuries ago.

It is featured on Iraq's 10,000-dinar banknote and gave its name to countless restaurants, companies and even sports clubs.

But in June 2014, it became infamous as the site where Baghdadi declared IS's "caliphate" just days after the jihadists seized Mosul in a lightning assault.

That capture prompted three years of ferocious fighting to wrest back Mosul and other Iraqi cities overrun by IS.

In June 2017, as Iraqi forces closed in on a shrinking IS-held pocket in Mosul's Old City, the jihadists blew up both the Al-Nuri mosque and its leaning minaret.

IS itself blamed a US-led strike for the destruction.

When the rest of the Old City fell back under state control, Iraqi forces celebrated at the mosque, holding IS's black flag upside down and tauntingly calling out, "Where is Baghdadi?"