Russian warplanes carried out intense air strikes on rebel strongholds in Syria on Friday hours before a ceasefire is due to come into force, the Syrian Observatory for Human Rights monitor said.

"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.

The partial ceasefire between regime forces and non-jihadist rebel fighters is due to come into force at midnight Friday (2200 GMT) Damascus time. The Islamic State group and the Al-Qaeda affiliated Al-Nusra Front are not included.

"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," he said.

Russian air strikes also hit the Daret Ezza area in western Aleppo province and Talbisseh city in Homs province.