Russian warplanes carried out intense air strikes on rebel strongholds in Syria on Friday hours before a ceasefire was due to come into force, the Syrian Observatory for Human Rights monitor said.
Russia dismissed the reports and said it was continuing strikes on "terrorist organizations" ahead of the truce.
The partial ceasefire between regime forces and non-jihadist rebel fighters is due to take effect at midnight Friday Damascus time. It does not include the Islamic State (ISIS) jihadist group and the Al Qaeda affiliated Nusra Front.
"From last night to this morning there have been Russian air strikes that are more intense than usual on rebel bastions including on Eastern Ghouta east of Damascus, in the north of Homs province and in the west of Aleppo province," Observatory head Rami Abdel Rahman said.
Air strikes in the non-jihadist rebel-held Qabtan al-Jabal area of Aleppo province killed eight members of the same family including three children on Thursday night, the monitor said.
"There were at least 25 air strikes on Eastern Ghouta," a main rebel bastion where the predominant opposition faction is the Jaish al-Islam movement, Abdel Rahman said.
"At least 10 of those hit Douma," an area there, said the Britain-based monitor, which relies of a wide network of sources in Syria.
"At the same time regime forces have violently shelled the city," Abdel Rahman said. "It's more intense than usual. It's as if they (the Russians and the regime) want to subdue rebels in these regions or score points before the ceasefire."
Russian air strikes also hit the Daret Ezza area in western Aleppo province and Talbisseh city in Homs province. In these areas, as in Ghouta, rebels outnumber Nusra fighters, the monitor said.
Kremlin spokesman Dmitry Peskov dismissed the Observatory's reports. "The Russian air force is certainly continuing its operation in Syria" but against "terrorist organizations," he said.
Since Moscow launched air strikes in Syria in September, it has been hitting non-jihadist rebel groups as it props up the regime of its ally Bashar al-Assad.
Abdel Rahman said the implementation of the partial truce will be complicated as Nusra are allied with rebels – Islamist and non-Islamist – in several parts of Syria.
Their "territories overlap especially in Idlib and Aleppo provinces. It will be very complex," Abdel Rahman said.
More than 270,000 people have been killed since the war erupted in March 2011, and millions have fled their homes.
AFP contributed to this report.