Fighter jets have bombed eastern areas of Syria's second city Aleppo, a BBC reporter near the city says.
The attack is seen as a significant escalation in the conflict.
It is thought to be the first time that warplanes have been used in Aleppo, our correspondent says.
Rebels launched an offensive against Aleppo at the weekend in an attempt to wrest control of the city from the army. Fierce fighting has been reported close to Aleppo's historic Old City.
Helicopter gunships were reportedly involved in the clashes earlier on Tuesday, the BBC's Ian Pannell says from the outskirts of Aleppo.
Pro-government troops bombarded the city, Syria's commercial centre, with shells and rocket fire as the government attempted to take back districts seized by the rebels.
A French correspondent there has spoken of rebels besieging a police headquarters close to the walls of the Old City, which is a world heritage site.
BBC News - Syria conflict: Aleppo bombed by fighter planes