It was the second straight day of Russian raids in Syria, where Moscow on Wednesday launched its first military engagement outside the former Soviet Union since the occupation of Afghanistan in 1979.

Russian President Vladimir Putin hit back at allegations that civilians had been killed, describing the claims as “information warfare”.

Moscow, a key backer of Assad, said the latest strikes had hit four targets linked to the Islamic State jihadist group, which controls large parts of Syria and neighbouring Iraq.

But a Syrian security source said they had targeted a powerful coalition of Islamist rebels which includes Al-Qaeda’s Syria affiliate and which is fiercely opposed to IS.

“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.

A member of the Army of Conquest, which controls Idlib province and has advanced west towards Assad’s coastal heartland of Latakia, said on Twitter that “Russian pigs” had flattened a mosque in Jisr al-Shughur.

In Moscow, the defence ministry said it had bombed “four Islamic State targets” in Syria overnight, destroying “the headquarters of terrorist groups and a weapons warehouse in Idlib area and a command centre… in Hama region.”

A car bomb factory north of Homs was also destroyed, it said.

Russia has rejected accusations its air strikes targeted moderate rebels fighting Assad.

Foreign Minister Sergei Lavrov challenged the United States to provide proof that Russia’s operation was not targeting “terrorists”.

US Senator John McCain said Thursday Russian warplanes had conducted strikes on groups “funded and trained by our CIA”.

He said the move showed Moscow’s real priority was “to prop up” Assad.

The head of Syria’s main opposition group accused Moscow of killing 36 civilians in the central province of Homs on Wednesday, but Lavrov denied any civilians were killed.

Russia’s defence ministry said fighter jets had carried out 20 sorties on Wednesday, striking “eight Islamic State targets” including a command post in the mountains.

– US-Russian military talks –

A US-led coalition has carried out near-daily air strikes on IS in Syria for more than a year.

The coalition said it had conducted one raid Wednesday in the northern province of Aleppo, destroying two excavators used by IS.

Washington complained that Moscow gave only an hour’s notice of the Russian strikes, but the two sides were preparing to hold military talks on the situation, perhaps as soon as Thursday.

After weeks of Russian military build-up in Syria, Russian senators on Wednesday unanimously approved armed intervention.

It remains unclear how much of the opposition fighting Assad’s army — including the Western-backed moderate opposition — is considered by Moscow as a potential target.

Kremlin spokesman Dmitry Peskov appeared to admit that Russia was targeting not only IS sites, saying it operates according to a list apparently agreed with the Syrian government.

“These organisations are known,” he was quoted as saying by Russian news agencies. “The targets are determined in coordination with the Syrian defence ministry.”

– ‘Ultimatums unrealistic’ –

Russia’s defence ministry said Moscow had sent more than 50 military aircraft as well as marines, paratroopers and special forces into Syria.

“More than 50 warplanes and helicopters are part of the Russian airforce striking Islamic State targets in Syria,” defence ministry spokesman Igor Konashekov told the Interfax news agency.

Russia and the West are in deep disagreement over Syria, with Moscow backing Assad while Western powers blame him for starting what has become a brutal war with more than 240,000 people dead and millions displaced.

Moscow has portrayed Assad as the only force stopping the spread of IS and argues that he must be part of the conflict’s political solution.

“Life has shown that it is unrealistic to give ultimatums demanding that Assad leaves in a situation when the country is in such a crisis,” Lavrov said.