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.
"Terrorists from Jabhat al-Nusra blow up the minaret of the Grand Umayyad Mosque in Aleppo," state television reported, saying rebels were seeking to "accuse the Syrian Arab Army" of carrying out the attack.
Activists uploaded video shot at the scene, showing the collapsed minaret, and rebels in the area 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 main opposition National Coalition also said an army tank had fired at the minaret, causing it to collapse.
"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.
"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," it added.
The Syrian Observatory for Human Rights confirmed the collapse of the minaret at the mosque, in Aleppo's Old City.
"The minaret of the Umayyad Mosque, around which violent clashes have raged in recent weeks, collapsed," said the Britain-based group.
There was no video immediately available showing the moment the minaret collapsed.
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 tank shell hit the minaret, it must have caused the mine to explode," he said.
Responding to regime claims that the jihadist Al-Nusra Front had blown up the minaret, Rifai said: "Why would an Islamist group blow up a minaret?"
The Umayyad mosque was originally built in the 8th century but was apparently destroyed and then rebuilt in the 13th century.
An archaeological treasure in Aleppo's UNESCO-listed Old City, the mosque has been the centre of fighting in recent months and already suffered extensive damage.
It recently came 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.