At least 12 members of the Islamic State group have been killed in Russia's first airstrikes on the jihadist faction's main Syrian bastion, a monitoring group said on Friday.
Russian air attacks also targeted the Army of Conquest, the most powerful Islamist coalition battling Syrian regime forces in the northwest, a security source on the ground said.
The defence ministry in Moscow confirmed it had carried out strikes on Raqa province on Thursday, as well as raids on the provinces of Aleppo in the north, Idlib in the northwest and Hama in central Syria.
The strikes are the first time Russia has targeted ISIS's stronghold in Raqa province, the de facto Syrian capital of its self-styled "caliphate."
Russia's defense ministry said Su-34 planes hit "an ISIS training camp near the village of Maadan Jadid", 70 kilometers (45 miles) east of Raqa city, and "a camouflaged command post at Kasrat Faraj, southwest of Raqa".
The Syrian Observatory for Human Rights said those strikes had killed at least a dozen ISIS fighters.
"Last night, Russian strikes on the western edges of Raqa city, and near the Tabqa military airport, killed 12 ISIS jihadists," Observatory head Rami Abdel Rahman said.
Activists and Raqa residents said ISIS had cancelled Friday prayers and emptied mosques there, fearing more Russian strikes.
"The residents are very afraid, especially if the Russians are going to operate like regime planes by targeting civilians," said activist Abu Mohammad who is from Raqa.
Speaking to AFP via the Internet, he said residents were staying indoors, and IS "has started to implement a plan to turn off electricity in a number of areas of the city when planes are overhead".
Moscow said Friday its warplanes had "conducted 18 sorties on 12 positions held by the Islamic State terrorist group in Syria" since Thursday.
The defense ministry said raids destroyed "a command post and communications center" held by IS in Daret Ezza in Aleppo province and "completely destroyed" bunkers and weapons depots in Maaret al-Numan and Habeet in Idlib province.
Russian raids also hit "an ISIS command post" in Kafr Zeita in Hama province.
According to the Observatory, ISIS does not control any of these areas. Kafr Zeita is held by Islamist rebels, while the areas in Idlib and Aleppo are held by ISIS's jihadist rival, Al-Qaeda's Syrian affiliate Al-Nusra Front.
Abdel Rahman had told AFP that seven civilians, including two children, were killed in Russian air attacks on Idlib province late Thursday.
According to several military sources and the Observatory, Russia continued its air strikes in several Syrian provinces on Friday.
A security source said that "Russian planes conducted several strikes on military positions and command centers held by the Army of Conquest in Jisr al-Shughur... and Jabal al-Zawiya in Idlib".
The Army of Conquest fiercely opposes both ISIS and President Bashar al-Assad's regime.
Headed by Al-Nusra, it controls all of Idlib province and has advanced on Assad's provincial stronghold of Latakia further west.
The Observatory confirmed that four Russian strikes had targeted Jabal al-Zawiya.
It said Russian raids on Khan Sheikhun in Idlib province had killed two Al-Nusra fighters, and that Latamina in Hama province had been hit as well.
A Syrian military source told AFP that Russian strikes on Friday targeted an ancient Christian town in Homs province seized by IS on August 5.
"Russian warplanes struck Al-Qaryatain this morning," the source said.
On Friday, ISIS launched a fierce attack on Syria's eastern city of Deir Ezzor and a nearby military airport, the Observatory said.
ISIS controls most of Deir Ezzor province and part of the city, but has tried for months to seize all of the provincial capital.
The latest violence came amid concerns that Russia is concentrating on groups opposed to Assad's embattled regime, instead of specifically targeting ISIS.
Moscow insists it is targeting ISIS and "other terrorist groups."