Syrian rebels led by Islamist groups have begun a massive assault that aims to take full control of the northern city of Aleppo, monitors report.
Rebels fired hundreds of rockets and missiles into government-held areas in a multi-district attack, the Syrian Observatory for Human Rights said.
It said the Syrian military had returned fire and launched air raids.
Analysts say the fall of Syria’s second city would be a major setback for President Bashar al-Assad.
The UK-based Observatory said that four civilians had been killed and more than 70 wounded in the rebel offensive, while five rebel fighters were killed in clashes with government forces in western Aleppo.
A statement by the rebel groups said their goal was to “liberate the city of Aleppo” and to ensure it would be ruled by Sharia principles.
A new alliance of rebel groups called Ansar Sharia is reportedly behind the assault on Aleppo. It includes the jihadist al-Nusra Front, al-Qaeda’s affiliate in Syria.
Control of Aleppo, Syria’s largest city and the country’s industrial and financial centre, has been divided between government and rebel forces since shortly after fighting began in Syria in 2012.
The government largely controls the west of the city, while different rebel factions are present in the east.
More than 230,000 people have been killed in Syria since its conflict began in March 2011.