Russia says it has greatly accelerated airstrike on what it calls “terrorist” targets in Syria and raised to 69 the number of its aircraft there.
But President Vladimir Putin said the current level of attacks was not enough to defeat so-called Islamic State (IS).
Russia said it fired cruise missiles for a fourth day against IS targets. The long-range missiles were launched from Caspian Sea warships.
Some missiles hit IS in strategically important Deir al-Zour, reports say.
The IS-held town in eastern Syria lies between the IS self-proclaimed capital of Raqqa and territory that the jihadists also control in neighbouring Iraq.
The Russian military says it fired 18 cruise missiles on Friday, destroying seven “Islamist” targets in Raqqa, Idlib and Aleppo provinces.
Col Patrick Ryder, a spokesman for US Central Command, said the Russian air strikes in recent days targeted more IS areas, including the group’s oil infrastructure.