Hundreds of shops were burning in an ancient covered market in Aleppo on Saturday as fighting between rebels and state forces in Syria's largest city threatened to destroy the UNESCO world heritage site.
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.
Fighting also continued to rage in Damascus where troops attacked several rebel areas in both the north and the south of the capital.
Violence across Syria, which began in March 2011 as peaceful protests, has killed more than 30,000 people, according to activist groups such as the Syrian Observatory for Human Rights.
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.
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.
The British-based Observatory for Human Rights, which has a network of activists across Syria, said President Assad's forces and rebels blamed each other for the blaze.
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.
Heavy clashes erupted outside several military sites in Aleppo on Saturday evening including at the Neirab military air base where activists said rebels were battling government forces.
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 President Assad.