BEIRUT, Lebanon — Fighting between Syrian insurgents and government forces in Aleppo left one of the Middle East’s most storied mosques severely damaged on Wednesday, its soaring minaret toppled by explosives. Each side accused the other of responsibility for the destruction at the Umayyad Mosque in Aleppo’s walled ancient city, a Unesco World Heritage site.

The mosque is considered an archaeological treasure but has been a battleground for months. It was first heavily damaged by fighting last October, and President Bashar al-Assad promised a restoration. But the military later retreated from the mosque and rebel fighters have occupied it since early this year.

Syria’s state media said the Nusra Front, an Islamic militant faction of the insurgency, had placed explosives inside the minaret, which dated from the 11th century. Anti-Assad activist groups at the site posted YouTube videos showing the rubble of the collapsed minaret strewn about the mosque’s tiled courtyard, with rebel fighters saying it had been hit by outside artillery fire as part of an attempt by Mr. Assad’s forces to rout them and retake the mosque.

“If he attacks all of the mosque, we will stay here, we will stick with our position, we won’t abandon our Islam even if all the world does,” one military commander says in a video.