Russia has bombed Syria for a third day, mainly hitting areas held by rival insurgent groups rather than the Islamic State (IS) fighters it said it was targeting and drawing an increasingly angry response from the West.

The US-led coalition that is waging its own air war against IS called on the Russians to halt strikes on targets other than IS.

"We call on the Russian Federation to immediately cease its attacks on the Syrian opposition and civilians and to focus its efforts on fighting ISIL (IS)," said the coalition, which includes the US, major European powers, Arab states and Turkey.

"We express our deep concern with regard to the Russian military build-up in Syria and especially the attacks by the Russian Air Force on Hama, Homs and Idlib since yesterday which led to civilian casualties and did not target Daesh (IS)," it said.

In Syria, the group is one of many fighting against Russia's ally, President Bashar al-Assad. Washington and its Western and regional allies say Russia is using it as a pretext to bomb other groups that oppose Assad. Some of these groups have received training and weapons from Assad's foreign enemies, including the US.

President Vladimir Putin held frosty talks with France's Francois Hollande in Paris, Mr Putin's first meeting with a Western leader since launching the strikes two days after he gave an address to the UN making the case to back Assad.

Friday prayers were cancelled in insurgent-held areas of Homs province that were hit by Russian warplanes this week, with residents concerned mosques could be targeted, said one person from the area.

"The streets are almost completely empty and there is an unannounced curfew," said the resident, speaking from the town of Rastan which was hit in the first day of Russian air strikes.

Warplanes were seen flying high above the area, which is held by anti-Assad rebels but has no significant presence of IS fighters. The terror group also cancelled prayers in areas it controls, according to activists from its de facto capital Raqqa.

Moscow said its latest strikes had hit 12 IS targets, but most of the areas it described were in western and northern parts of the country, while IS is mostly present in the east.

The Russian Defence Ministry said its Sukhoi-34, Sukhoi-24M and Sukhoi-25 warplanes had flown 18 sorties hitting targets that included a command post and a communications centre in the province of Aleppo, a militant field camp in Idlib and a command post in Hama.

The UK-based Syrian Observatory for Human Rights, which monitors the conflict with a network of sources on the ground, said there was no IS presence at any of those areas.

Russia has however also struck IS areas in a small number of other attacks further east. The Observatory said 12 IS fighters were killed near Raqqa on Thursday, and planes believed to be Russian had also struck the Islamic State-held city of Qarytayn.

Russia has said it is using its most advanced plane, the Sukhoi-34, near Raqqa, the area where it is most likely to encounter US and coalition aircraft targeting IS.