Russia bombed Syria for a third day on Friday, mainly hitting areas held by rival insurgent groups rather than the Islamic State 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 Islamic State called on the Russians to halt strikes on targets other than the Islamic State.
"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," said the coalition, which includes the United States, 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," it said.
ISIL and Daesh are both acronyms for the Islamic State, also known as ISIS, which has set up a caliphate across a swathe of eastern Syria and northern Iraq.
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 United States.
President Vladimir Putin held frosty talks with France's Francois Hollande in Paris, Putin's first meeting with a Western leader since launching the strikes two days after he gave an address to the United Nations making the case to back Assad.
Friday prayers were canceled in insurgent-held areas of Homs province that were hit by Russian warplanes this week, with residents concerned that 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 Islamic State fighters.
The Islamic State also canceled prayers in areas it controls, according to activists from its de facto capital Raqqa.
A Russian air strike on Thursday destroyed a mosque in the town of Jisr al-Shughour, captured from government forces by an alliance of Islamist insurgents earlier this year, activists said.
Moscow said on Friday its latest strikes had hit 12 Islamic State targets, but most of the areas it described were in western and northern parts of the country, while Islamic State is mostly present in the east.
The Russian Defense 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 center 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 Islamic State presence at any of those areas.
Russia has however also struck Islamic State areas in a small number of other attacks further east. The Observatory said 12 Islamic State 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 Islamic State.
As Hollande hosted Putin in Paris, both men looked stern and frosty-faced in the yard of the Elysee palace, exchanging terse handshakes for the cameras.
An aide to Hollande said they "tried to narrow differences" over Syria during talks that lasted more than an hour.
Hollande laid out France's conditions for supporting Russian intervention, which include a halt to strikes on groups other than the Islamic State and Al-Qaeda, protections for civilians and a commitment to a political transition that would remove Assad.
Putin's decision to launch strikes on Syria marks a dramatic escalation of foreign involvement in a 4-year-old civil war in which every major country in the region has a stake.
Lebanese sources have told Reuters that hundreds of Iranian troops have also arrived in recent days in Syria to participate in a major ground offensive alongside government troops and their Lebanese and Iraqi Shi'ite militia allies.
Common enemy, different friends
Western countries and Russia say they have a common enemy in the Islamic State. But they also have very different friends and opposing views of how to resolve a war that has killed at least 250,000 people and driven more than 10 million from their homes.
Washington and its allies oppose both the Islamic State and Assad, blaming him for attacks on civilians that have radicalized the opposition and insisting that he has no place in a post-war settlement.
Russia says Assad's government should be the centerpiece of international efforts to fight militants.
The campaign is the first time Moscow has sent forces into combat beyond the frontiers of the former Soviet Union since the disastrous Afghanistan campaign of the 1980s, a bold move by Putin to extend Russia's influence beyond its neighborhood.
It comes at a low point in Russia's relations with the West, a year after the United States and EU imposed financial sanctions on Moscow for annexing territory from Ukraine.
Assad and his father before him were Moscow's close allies in the Middle East since the Cold War, and Russia maintains its only Mediterranean naval base on the Syrian coast.
Moscow's intervention comes at a time when insurgents had been scoring major battlefield gains against government forces after years of stalemate in the war.
Putin appears to be betting that by defending Assad he can increase Russia's influence in any post-war settlement, safeguard the naval base and counter the influence of regional rivals like NATO member Turkey. He may also intend to reinforce his image at home as a strong leader willing to challenge global rivals, first and foremost the United States.