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.
Deir al-Zour province is also rich in oil.
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.
But he added that "the majority of Russian air strikes are still against moderate Syrian opposition forces, which is clearly concerning, and those strikes are in support of the Syrian regime" of President Bashar al-Assad.
`Revenge for our dead`
A monitoring group, the Syrian Observatory for Human Rights, said Syrian and Russian warplanes conducted 50 bombing raids in Deir al-Zour province - Russia`s most intense assault there to date.
The BBC`s Steve Rosenberg in Moscow says that in the Russian defence ministry video soldiers can be seen writing messages on the bombs before loading them onto the aircraft - phrases like: "This is revenge for our dead" and "This is for Paris".
""In four days of heavy bombing against IS, the ministry said, more than 100 cruise missiles were launched and more than 800 "terrorist" targets destroyed in Syria.
Mr Putin said Russia still faced a lot of work. He expressed hope that the next phases would "produce the expected result", but did not clarify what those phases would be.
Later the president`s spokesman told the BBC there was no talk of putting troops on the ground in Syria.
IS said its jihadists based in Sinai brought down a Russian Metrojet airliner in Egypt last month. Russia concluded that it was a bomb that blew up the plane, killing 224 people, nearly all of them Russians.
Russia`s air campaign in Syria began on 30 September. It fired its first cruise missiles in the conflict on 17 November.
Turkey warns Russia
Meanwhile, Turkey has warned Russia that it must immediately stop bombing "civilian Turkmen villages" in Syria, close to the Turkish border.
The Russian ambassador to Ankara was summoned to the Turkish foreign ministry to hear the protest.
Turkey warned that bombing villages populated by the Turkmen minority could lead to "serious consequences".
Syrian government forces backed by Russian aircraft launched a ground offensive on the mainly Turkmen villages in Bayir Bucak, north-west Latakia province, on Thursday, Turkey`s Anadolu news agency reported.
The Turkish government is vehemently opposed to President Assad, while Russia says its air campaign is justified because Mr Assad has requested it.
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