At least 23 civilians were killed in the Syrian opposition redoubt of Eastern Ghouta, near Damascus, with the majority of victims perishing in Russian air raids, a monitor said.
The Britain-based Syrian Observatory for Human Rights told AFP that 18 people were killed by Russian strikes in the town of Misraba, while the remainder died in shelling from government forces.
Observatory head Rami Abdel Rahman said three children and 11 women were among those killed.
The war in Syria has killed more than 340,000 people and displaced millions from their homes since it began in 2011 with the brutal repression of anti-government protests.
Eastern Ghouta, a small enclave east of the capital Damascus, is controlled mostly by rebels from the Jaish al- Islam group.
Russia first launched bombing raids in 2015 in support of Syrian President Bashar al-Assad’s beleaguered forces.
Those strikes have helped Assad regain control over much of war-ravaged Syria.
The Observatory relies on a network of sources inside Syria and says it determines whose planes carry out raids according to type, location, flight patterns and munitions used.