Russian jets pounded several opposition-held parts of eastern Aleppo, killing 26 people and reducing the areas to rubble. Fifteen others were killed in two more incidents of violence.
After a lull of several days, Russian jets resumed heavy bombing of eastern Aleppo on Tuesday, killing 26 people.
The bombing by Russian jets mostly targeted several neighbourhoods in the opposition-held parts of Aleppo, reducing the areas to rubble. Up to 300,000 people are still believed to be in the besieged parts of the country's largest city.
Russia and the Syrian regime had reduced air raids in the northern city over the last week. Regime forces said it was partly to allow civilians to leave opposition-held eastern neighbourhoods.
The regime previously said that opposition holed up in Aleppo can leave with their families if they lay down their arms, but the opposition has denounced that offer as a deception.
Regime leader Bashar al Assad vowed to completely recapture Aleppo, which has been divided between the regime and opposition control since the war began in 2011.
A brief a brief ceasefire between the Russian-backed regime and US-backed opposition groups that was mediated by Washington and Moscow collapsed last month.
Children killed in school incident
In another incident, at least five people, including children, were killed when a shell belonging to opposition forces struck a school in Deraa, the Britain-based Syria Observatory for Human Rights (SOHR) monitoring group said.
The attack left 20 others wounded, the SOHR added.
Control of Deraa remains divided between the Syrian regime and opposition forces.
At least 10 people were also killed and another 20 wounded when a DAESH suicide bomber blew himself up in a village in northern Syria in the early hours of Tuesday, the SOHR said.
The blast took place in al-Mashi, which is in the countryside around the city of Manbij, which has been under YPG control since August.