Mosul (Iraq) - Mosul's trademark leaning minaret was missing from its skyline for the first time in centuries Thursday after desperate militants blew it up as Iraqi forces advanced on an ancient mosque compound. Explosions on Wednesday evening levelled the Nuri mosque where Abu Bakr al-Baghdadi gave his first sermon as leader of ISIS and its ancient leaning minaret, known as the "Hadba" (Hunchback). Officials from Iraq and the U.S.-led anti-ISIS coalition said the destruction of the site was a sign of the militant group's imminent loss of Mosul, with Prime Minister Haider al-Abadi calling it an "official declaration of defeat". The loss of the unmistakeable 12th century minaret, one of the country's most recognisable monuments sometimes referred to as Iraq's Tower of Pisa, left the country in shock. But the destruction had been widely anticipated, with commanders saying ISIS, also known as ISIS and Daesh, would not have allowed Iraqi forces to score a hugely symbolic victory by recapturing the site.