Air strikes on the northern Syrian city of Raqqa and its outskirts over the past three days are reported to have killed at least 33 fighters with the Islamic State group.
The Britain-based Syrian Observatory for Human Rights said the militants were mostly killed when checkpoints were attacked by French and other planes.
The French defence ministry said 10 jets hit two IS command centres in the militants’ base in Raqqa.
France has launched waves of air strikes after attacks claimed by IS killed at least 129 people in Paris on Friday.
The Observatory said more Islamic State fighters are believed to have been killed in the strikes, but their bodies were so severely dismembered it was not possible to give a figure.
The Paris attacks have galvanised international determination to confront Islamic State in Syria and Iraq, bringing France, Russia and the US closer to an alliance.
Russian President Vladimir Putin has ordered the missile cruiser Moskva, currently in the Mediterranean, to start co-operating with the French military on operations in Syria.
US president Barack Obama has said he is taking a wait-and-see approach on whether Russia does more to focus on IS targets, which America would “welcome”.
Russia intensified air strikes on Raqqa on Tuesday after Moscow’s FSB security service confirmed for the first time that a bomb caused the October 31st crash of a Russian airliner over Egypt’s Sinai desert, killing 224 people. IS had already claimed responsibility.
Russia recently joined the international campaign of air strikes against the Islamic State, but Mr Obama maintained that Moscow had been more focused on targeting moderate opposition groups and propping up Syrian president Bashar Assad.
Mr Obama said he expressed his view to Mr Putin that Russia had been going after the wrong targets.
He said the US was “going to wait and see” whether Moscow shifted its focus to IS targets “and if it does so, that’s something we welcome”.
US secretary of state John Kerry said a ceasefire between Syria’s government and the opposition could be weeks away. He described it as potentially a “gigantic step” toward deeper international co-operation against IS.