Hundreds of shops were burning in the ancient covered market in Aleppo on Saturday as fighting between rebels and state forces in Syria's largest city threatened to destroy a UNESCO world heritage site.
The uprising-turned-civil war that is now raging across Syria has killed more than 30,000 people, according to activist groups such as the Syrian Observatory for Human Rights.
But beyond the dramatic human cost, many of Syria's historic treasures have also fallen victim to an 18-month-old conflict that has reduced parts of some cities to ruins.
Rebels fighting to topple President Bashar al-Assad announced a new offensive in Aleppo, Syria's commercial hub of 2.5 million people, on Thursday, but neither side has appeared to make significant gains.
In Aleppo, activists speaking via Skype said army snipers were making it difficult to approach the Souk al-Madina, the medieval market of vaulted stone alleyways and carved wooden facades in the Old City, once a major tourist attraction.
Videos uploaded to YouTube showed dark black clouds hanging over the city skyline.
Activists said the fire might have been started by shelling and gunfire on Friday and estimated that between 700 and 1,000 shops had been destroyed so far. The accounts were difficult to verify because of government restricts on foreign media.
Aleppo's Old City is one of several locations in Syria declared world heritage sites by UNESCO, the United Nations cultural agency, that are now at risk from the fighting.
UNESCO believes five of Syria's six heritage sites – which also include the ancient desert city of Palmyra, the Crac des Chevaliers crusader fortress and parts of old Damascus – have been affected.
The British-based Observatory for Human Rights, which has a network of activists across Syria, said Assad's forces and rebels blamed each other for the blaze.
Heavy clashes erupted outside several military sites in Aleppo on Saturday evening. Activists said rebels were battling government forces outside the Neirab military air base.
The Observatory said clashes outside a base used for artillery training had set a nearby building alight and killed three people.
Fighting was also reported outside Bab Antakya, a stone gateway to Aleppo's Old City, which sits on ancient trade routes and survived a parade of rulers throughout its construction between the 12th and 17th century.
Rebels said they had taken the gate, but some activists said the fighting continued and neither side was truly in control.
"No one is actually making gains here, it is just fighting and more fighting, and terrified people are fleeing," said an activist contacted by telephone who declined to be identified.
He said in some districts, bodies were lying in the streets and residents would not collect them, fearing snipers.
More than 40 people had been killed in fighting across Syria, according to the Observatory.
Syria's military deadlock is also reflected diplomatically, with foreign powers stalemated over how to act. Western states and Gulf Arab countries back the opposition but most seem reluctant to interfere, while Russia, China and Iran back Mr. al-Assad.
The revolt against four decades of Assad family, which began in March, 2011, as peaceful protests, has become an armed insurgency, with rebels holding ground in Aleppo and rural towns of northern Syria.
The fighting has crept closer to Syria's border zones, and some bullets and rockets have hit neighbouring Lebanon, Iraq and Turkey. Ankara warned it would take action if its territory was again hit – a mortar bomb hit a town on its southeastern frontier on Friday.
An advisor to Iran's Supreme Leader Ayatollah Ali Khamenei said he was confident Syria's government would beat the rebels.
"The victory of the government of Syria against internal opponents, America, and their other Western and Arab supporters, is counted as a victory of the Islamic Republic of Iran," said Ali Akbar Velayati, according to state news agency IRNA.
"The victory of the Syrian government is certain."
Activists reported fresh clashes in the capital Damascus and its suburbs and said security forces were torching homes as helicopters buzzed overhead.
The bloodied bodies of at least 12 men were found in Damascus's northwestern suburb of Qudsaya. A video published by showed rows of men, some of them apparently shot, laid in a room whose walls were spattered with blood.
Some Damascus residents have accused government forces of summary executions in rebel districts.
"They can't arrest everyone, so they are using elimination tactics. They enter area that was held by rebels, look for people that are wanted and kill them all," one activist said.
Mr. al-Assad has long defended the fierce crackdown, arguing that he has been fighting Islamist militants funded from abroad.
Text messages attributed to the army were sent to all Syrian mobiles since Aleppo rebels announced their new offensive.
"To those who have implicated themselves against the state: Those who have offered you money have left you with two options: You will be killed fighting the state or it will kill you to get rid of you," one message read.
"The state is more merciful than you. Think and decide. The Syrian Army."