Heavy fighting gripped the outskirts of Syria's second city Aleppo on Thursday after air strikes pounded rebel-held districts through the night triggering major fires.
Opposition activists accused the Syrian government and its Russian ally of dropping incendiary bombs as volunteer firefighters battled to contain the blazes in the already devastated city.
An AFP correspondent in the rebel-held east of the city reported that his entire street had been in flames following the pre-dawn strikes.
An alliance of jihadists and Islamist rebels has been battling to break the government's siege after sustaining a major reverse earlier this month.
Fierce fighting rocked the Ramussa district on the southwestern outskirts where the rebels briefly opened a relief line last month, the Syrian Observatory for Human Rights said.
Rebel mortar fire hit government-held neighbourhoods, the Britain-based monitoring group said. It had no immediate word on any casualties.
Air strikes on east Aleppo on Wednesday killed 12 civilians, two of them children, the highest death toll in the city since the collapse of a week-long ceasefire earlier this week.
The failure of the truce brokered by Moscow and Washington has seen a surge of fighting on all of the major battlefronts of Syria's five-year-old civil war.
An AFP correspondent in the rebel-held eastern suburbs of the capital Damascus reported shelling and air strikes early on Thursday.
Fighting was also reported in the central provinces of Homs and Hama.
Russia and the United States were to co-chair a meeting of the 23-nation International Syria Support Group in New York later on Thursday in a last-ditch bid to salvage the failed ceasefire.
AFP contributed to this report