French and Russian air strikes in Syria have killed at least 33 Islamic State (Isis) militants, a monitoring group said.

Many IS fighters were also wounded in strikes on weapons depots, barracks and checkpoints in the jihadist group's Syrian base of operations, Raqqa, the Syrian Observatory for Human Rights told AFP.

It was the third night in a row that IS targets have been hit by French warplanes, with the country stepping up its campaign against IS in the wake of terror attacks in Paris in which at least 129 people were killed.

Russian warships and missiles also pounded Isis targets with bombs, after Russian authorities confirmed that a terrorists bomb brought down a Russian airliner in the Sinai peninsula on 31 October, with Russian President Vladimir Putin pledging revenge for the attack.

"The limited number of deaths can be explained by the fact that the jihadists had taken precautions," said Abdel Rahman, director of the observatory, which collects information from a number of contacts in Syria.

"There were only guards around the depots and barracks and most of those killed were at the checkpoints."