Activists have said Syrian government forces launched a counterattack against rebel groups who had seized new parts of the besieged city of Aleppo.
The fighting on October 29 came a day after insurgent fighters staged a surprise attack, aimed at breaking the government siege on the eastern districts that are largely controlled by opposition groups.
The British-based Syrian Observatory for Human Rights said Syrian troops backed by Russian and Syrian air cover, attacked some of the western districts seized earlier by the rebel forces.
The Syrian Army said it was also using artillery and rockets to hit one district known as Assad.
East Aleppo, where the United Nations estimates 275,000 people are trapped. has been ravaged by a campaign of air strikes by Russian and Syrian forces.
Rebel forces include moderate groups, some of which are backed by the United States and its allies, along with terrorist groups.
The struggle for Aleppo is shaping up to be one of the most strategic battles of a war that has lasted nearly six years and killed hundreds of thousands.