At least 28 civilians were killed on Wednesday in the Syrian opposition stronghold of Eastern Ghouta, near Damascus, most of them in Russian air raids.
According to the Britain-based Syrian Observatory for Human Rights 19 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 seven children and 11 women were among those killed.
Victims were taken to a hospital in Douma where rescuers were bringing in mostly women and children.
Medical staff tried to revive an infant who had been pulled from the rubble, but without success. A young girl among the wounded received stitches for a serious injury to her face.
"Among the wounded were two women in their twenties. One of them lost both eyes and the other lost one eye," said a medical source at the hospital.
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. The strikes have helped Assad regain control over much of the war-ravaged country.
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.
The latest raids came after at least seven civilians, including five children, were killed Tuesday by air strikes in northwestern Idlib province, the last outside government control, the Observatory said.
Government and allied forces backed by Russian warplanes have been battling jihadist fighters and rebels for more than a week in an area straddling the boundary between Idlib and Hama provinces.
The government push on the edge of Idlib province follows two months of sporadic fighting that the United Nations says has displaced more than 60,000 people.
Idlib province, held by Tahrir al-Sham, was one of four "de-escalation zones" agreed to help halt fighting around Syria by regime backers Russia and Iran and rebel supporter Turkey.
Observers say government forces first aim to take control of the southeast of Idlib province, allowing the regime to have full control of a road that links the capital Damascus to the government-held second city of Aleppo.
According to a report by the Syrian Network for Human Rights (SNHR) Mr Assad's regime has dropped almost 70,000 barrel bombs between 2012 and 2017. The worst-hit areas have been civilian population centres.
Russia denied on Thursday a report in the daily newspaper Kommersant that seven Russian planes had been destroyed by rebel shelling at Syria's Hmeymim air base on December 31, Russian news agency TASS quoted the defence ministry as saying. The report cited two "military-diplomatic" sources.
The ministry also said two Russian service personnel were killed in a mortar attack on the base by rebels.
Earlier on Wednesday Moscow's defence ministry said a Russian helicopter crashed in Syria on New Year's Eve killing both pilots following a technical fault.
The Mi-24 military helicopter was flying to Hama, northwestern Syria, and there was no firing from the ground, agencies quoted the ministry as saying.
"Both pilots died in a hard landing 15 km from the air base," the ministry said, adding that a technician had been injured and taken to another air base for emergency treatment.
Russia's Defence Minister Sergei Shoigu last month said the military had completed the partial withdrawal from Syria ordered by president Vladimir Putin, but Moscow would maintain a presence in the country, including three battalions and two bases.
Moscow acknowledged in recent months that its special forces are also active on the ground in the offensive against Islamic State jihadists.
Meanwhile the leader of Lebanon's Iran-backed Hezbollah group said the Syrian war, now in its seventh year, will be finished in one or two years at most.
In an interview with Lebanon's pro-Iran al-Mayadeen channel on Wednesday Sayyed Hassan Nasrallah also said Israeli strikes on Hezbollah positions in Syria did not, and will not, prevent supplies of weapons reaching the group.
Hezbollah and other Iran-backed groups have backed Syria's President Bashar al-Assad during the conflict which erupted in 2011.