An international court on Tuesday found a Muslim radical guilty of committing a war crime by overseeing the destruction of historic mausoleums in the Malian desert city of Timbuktu, and sentenced him to nine years in prison.

Ahmad Al Faqi Al Mahdi, a former teacher, had pleaded guilty and expressed remorse for his role in overseeing the destruction of nine mausoleums and a mosque door by pickax-wielding rebels in June and July of 2012.

His trial, which opened Aug. 22, was a landmark for the International Criminal Court, which has struggled to bring suspects to justice since its establishment in 2002. It was the tribunal's first conviction for destruction of religious buildings or historic monuments, and the first guilty verdict delivered against a Muslim extremist.

U.N. Secretary-General Ban Ki-moon welcomed the court's ruling as "an important step forward in the fight against impunity in Mali," according to a statement released by Ban's spokesman.

Al-Qaida-linked rebels occupied the fabled Saharan city of Timbuktu in 2012 and enforced a strict interpretation of Islamic law that included destruction of the historic mud-brick tombs they considered idolatrous. Al Mahdi was leader of one of the "morality brigades" set up by Timbuktu's new rulers.

ICC prosecutors said Al Mahdi was a member of Ansar Eddine, an Islamic extremist group with links to al-Qaida that held power in northern Mali in 2012. The militants were driven out after nearly a year by French forces, which arrested Al Mahdi in 2014 in neighboring Niger.