* Market is part of UNESCO heritage site
* Activists say neither rebels nor army advancing in Aleppo
* More than 40 killed by Saturday afternoon
By Erika Solomon
BEIRUT, Sept 29 (Reuters) - Hundreds of shops were burning in the ancient covered market of the Old City of 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 like 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 that was 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 heavy shelling and gunfire on Friday and estimated that 700 to 1,000 shops had been destroyed so far. The accounts are difficult to verify because the government restricts access to 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, which has a network of activists across Syria, said Assad’s forces and rebels were blaming each other for the blaze.
Activists also reported heavy clashes at Bab Antakya, a stone gateway to Aleppo’s old city, which sits on ancient trade routes and has survived a parade of rulers throughout its construction between the 12th and 17th century.
Rebels said they had taken control of the gate, but some activists said the fighting there was continuing 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 named.
He said bodies were lying in the streets and residents were not going out to collect them for fear of snipers.
By noon on Saturday, 40 people had been killed in fighting across Syria, according to the Observatory.
The bloodshed in Syria has escalated since rebels took their fight to the major cities. Activists reported fresh clashes in the capital Damascus and surrounding suburbs and said security forces were torching homes as helicopters buzzed overhead.
The revolt, which began in March 2011 as peaceful protests, has become an armed insurgency that is now able to hold ground in Aleppo and rural towns of northern Syria, close to the Turkish border, but can do little to fend off Assad’s air force and artillery.
Assad has defended the fierce crackdown that spawned the armed rebellion, arguing that he has been fighting Islamist militants funded from abroad.
One activist contacted by phone read out text messages that have been sent to all Syrian mobiles since rebels in Aleppo announced their new offensive. The text messages called on the rebels to surrender.
“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.”