Ancient Syrian market being consumed in fire started by fighting Shaam News Network via AP In this image taken from video obtained from Shaam News Network, which has been authenticated based on its contents and other AP reporting, a fire rages at the medieval market in Aleppo, Syria. Hundreds of shops in the ancient covered market in Aleppo, Syria, were burning Saturday as fighting between rebels and state forces in Syria's largest city threatened to destroy the U.N. World Heritage Site. 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, Reuters reported. Activists said the fire might have been started by shelling and gunfire, and estimated that between 700 and 1,000 shops had been destroyed so far. The accounts were difficult to verify because of government restrictions 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. UNESCO believes five of Syria's six World Heritage Sites -- which include the ancient desert city of Palmyra, the Crac des Chevaliers crusader fortress, and parts of old Damascus -- have been affected by the fighting. The British-based Syrian Observatory for Human Rights said Syrian forces and rebels blamed each other for the blaze. The uprising-turned-civil war has killed more than 30,000 people, according to activist groups. Rebels fighting to topple President Bashar al-Assad on Thursday announced a new offensive in Aleppo, Syria's commercial hub of 2.5 million people, but neither side has appeared to make significant gains. Text messages attributed to the army were sent to all Syrian mobile phones when the offensive was announced. "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. Activists also reported heavy clashes at 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 centuries. "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. By noon on Saturday, 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 Assad. The revolt, 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 neighboring 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. 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. Assad has long defended the fierce crackdown, arguing that he has been fighting Islamist militants funded from abroad.