Heavy government bombardment of rebel-held towns across Syria on Friday killed at least 56 civilians, more than a quarter of them children, a monitoring group said.
The bloodiest attacks were in Eastern Ghouta, a rebel stronghold east of Damascus, where at least 41 civilians were killed, the Syrian Observatory for Human Rights said.
"Regime warplanes targeted the towns of Jisreen and Kfar Batna in the Eastern Ghouta region", leaving 35 killed, the Britain-based Observatory added.
Six children were among the dead there and dozens of people were wounded.
But the opposition National Coalition, the leading anti-regime group in exile, blamed the Jisreen strikes on Russia.
"Russian warplanes targeted a public market… leaving 11 killed and 50 wounded" in Jisreen, the Coalition tweeted.
Another six civilians, including two children, were killed in regime rocket fire on the flashpoint Eastern Ghouta town of Douma, the Observatory said.
Government forces regularly bombard Eastern Ghouta, a populated suburb of Damascus largely controlled by the powerful Jaish al-Islam rebel group.
In a video posted by an online activist group in Jisreen, a distressed man in a debris-strewn street screamed: "Syrian flesh for sale!"
And footage posted by the local SMART news agency depicted men carrying bloodied victims out of destroyed buildings on stretchers as sirens wailed.
Eleven people, four of them children, were killed in government air strikes on the opposition-held town of Talbisseh in central Syria, according to the Observatory said.
In the southern province of Daraa, four children were killed when the regime bombarded the town of Hara.
And four civilians died in shelling of Sanamayn, 30 kilometres (20 miles) east of Hara.
Observatory director Rami Abdel Rahman could not specify if the Sanamayn attack was by regime or rebel forces.
Also on Friday, at least 14 Islamic State group jihadists were killed in an air raid in the northeastern province of Hasakeh, the Observatory said.
The monitor said it was likely the US-led coalition had conducted the strikes, which targeted a school that the group had taken over as a base.
The Observatory relies on a network of activists, medical staff and fighters on the ground who identify warplanes based on model, flight patterns and munition types.
Syria\’s conflict has taken the lives of more than 250,000 people, and another four million have been forced to flee since it erupted in March 2011.
Beginning as an uprising against President Bashar al-Assad, the conflict has evolved into a multi-front war increasingly dominated by jihadist fighters.
IS has seized swathes of territory across northern, central, and eastern Syria, but rebels, Kurdish militia and the US-led coalition as well as Russian warplanes have sought to fight them back.