The minaret of Aleppo's ancient Umayyad mosque was destroyed on Wednesday, Syrian state media and a watchdog reported, with the regime and the opposition blaming each other.
An archaeological treasure in Aleppo's UNESCO-listed Old City, the mosque has been the centre of fighting for months and had already suffered extensive damage.
With insurgents and the regime caught in a stalemate in the key northern city, the ancient mosque has fallen in and out of rebel hands several times.
The Umayyad mosque was originally built in the 8th century but was apparently destroyed and then rebuilt in the 13th century.
It has recently fallen back into rebel hands, but has been left pockmarked by bullets and stained with soot.
Antique furnishings and intricately sculpted colonnades have been charred, valuable Islamic relics ransacked and ancient artefacts -- including a box purported to contain a strand of the Prophet Mohammed's hair -- looted.
Rebels say they have managed to salvage ancient handwritten Koranic manuscripts and have hidden them.
On Wednesday, as reports broke of the minaret's destruction, activists uploaded video shot at the scene, but there was no video immediately available showing the moment of the blast that caused the collapse.
As with multiple other attacks in Syria's spiralling conflict, which the UN says has left more than 70,000 people dead, the regime and the opposition blamed each other for the damage.
State media said jihadist Al-Nusra Front fighters blew up the minaret, and accused the group classed by the United States as a "terrorist" organisation of seeking to blame loyalist forces.
But rebels, the opposition and activists all said the army was responsible.
"Tanks began firing in the direction of the minaret until it was destroyed," one rebel said in a video posted on YouTube, insisting rebel snipers were not stationed inside the minaret.
"We were afraid that it would be targeted," he said.
"The Assad regime has done everything it can to destroy Syria's social fabric. Today, by killing people and destroying culture, it is sowing a bitterness in people's hearts that will be difficult to erase for a very long time," the video added.
Meanwhile, an activist who identified himself as Zain al-Rifai said he saw an army tank "fire several shells directly at the Umayyad mosque, including at the minaret".
He also claimed the force of the explosion was magnified because of landmines planted by the army in the mosque complex before the rebel takeover.
"When the army was in control of the mosque, it planted mines across the complex. When the rebels took over, they demined the area, but couldn't come near the minaret for fear of snipers.
"When the tank shell hit the minaret, it must have caused the mine to explode," said Rifai, who works with the Aleppo Media Centre, a network of citizen journalists on the ground.
Responding to regime claims that the jihadist Al-Nusra Front had blown up the minaret, Rifai asked: "Why would an Islamist group blow up a minaret?"
The main opposition National Coalition, recognised by dozens of states and organisations as the legitimate representative of the Syrian people, mourned the ancient minaret's destruction.
"The deliberate destruction of this minaret, under whose shadow Saladin... and (10th century Iraqi poet) Al-Mutanabbi rested, is a crime against human civilisation," said the Coalition.