Photo: The Canadian Press

The Islamic State group blew up a historic landmark in Iraq — Mosul's famed 12th century al-Nuri mosque with its iconic leaning minaret known as al-Hadba, from where the IS leader proclaimed the militant group's self-styled caliphate nearly three years ago.

The explosion destroyed another piece of priceless Iraqi cultural heritage.

Iraq's Ministry of Defence said the militants detonated explosives planted inside the structures on Wednesday night. Prime Minister Haider al-Abadi tweeted early on Thursday that the destruction was an admission by the militants that they are losing the fight for Iraq's second-largest city.

"It is a shock, a real big shock," Amir al-Jumaili, a professor at the Archaeology College in Mosul told The Associated Press.

The IS blew up the mosque during the celebrations of Laylat al Qadr, the holiest night of the year for Muslims. The "Night of Power" commemorates the night the Qur’an was revealed to the Prophet Muhammad during the Muslim holy month of Ramadan, which is now underway.