Fresh Russian air strikes Thursday targeted bases held by a powerful Islamist rebel coalition including Al-Qaeda's affiliate in northwest Syria, a Syrian security source said.
"Air strikes from four Russian warplanes struck bases held by the Army of Conquest in Jisr al-Shughur and Jabal al-Zawiya in Idlib province," the source said, adding that arms depots held by "armed groups" in neighbouring Hama province were also targeted.
The Army of Conquest has seized all of Idlib province and has advanced west towards Latakia, the stronghold province of embattled Syrian President Bashar al-Assad.
The alliance is also fiercely opposed to ISIS group, which Russia insists it is targeting.
On Twitter, a member of the Army of Conquest said "the alliance of Russian pigs launched its operations... by destroying a mosque in Jisr al-Shughur and flattening it."
Russia launched its first air strikes in war-torn Syria on Wednesday, striking opposition-held areas in the central provinces of Homs and Hama.
Russian Foreign Minister Sergei Lavrov said the Russian military has only struck "terrorist groups," but France and the United States immediately expressed doubts that Moscow was targeting ISIS.
The head of Syria's main opposition group accused the Kremlin of aiming to support Assad's regime and killing 36 civilians in the central province of Homs on Wednesday.