A suspected Russian air strike on a home in the countryside near the central city of Homs has killed 48 people from a single family, Syrian activists said.
The bomb shelter where the family was hiding was hit by a rocket on Saturday, activists told Al Jazeera on Sunday.
Rescue teams spent over 10 hours trying to recover the bodies of the victims, Al Jazeera was told.
Abu Abbas, a survivor, said the majority of the casualties were children.
"The eldest of the victims is a 70-year-old woman; the youngest was a one-month-old child," Abu Abbas said.
"They were not terrorists as [Russian President Vladimir] Putin said."
Moscow has been launching air strikes in the area in addition to various other regions of the country.
In a statement on Saturday, the Russian military said its air force made 36 sorties, hitting 49 Islamic State of Iraq and the Levant (ISIL) group targets in Syria in the last 24 hours.
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The targets were hit in Hama, Idlib, Latakia, Damascus, and Aleppo regions, the statement said.
In another development on Saturday, Syrian government forces edged forward in the northern province of Aleppo with air cover from Russian warplanes, but faced fierce resistance from rebel forces in the country's centre.
Since Moscow began its air campaign in support of its Damascus ally on September 30, the army and its allies have launched four ground offensives against rebel forces in northern and central Syria.
The assaults were part of the latest push forward in the conflict that has killed more than 250,000 people, according to rights groups.
Syrian troops have gone on the attack in Aleppo, Hama, Homs and Latakia provinces, taking advantage of Russian air strikes against al-Nusra Front, an al-Qaeda affiliate, and other rebel groups.
Source: Al Jazeera and agencies