Beirut (AFP) - Russia on Saturday pressed ahead with its aerial campaign in Syria, bombing the Islamic State group's stronghold after the United States and its allies accused Moscow of targeting moderate rebel groups.

A staunch backer of Syria's embattled leader Bashar al-Assad, Russia began sorties over its Soviet-era ally on Wednesday in what it said would be a prolonged bombing campaign against IS and other extremist groups.

The United States and its allies immediately slammed Moscow's intervention, accusing the Kremlin of seeking to buttress Assad under cover of a claimed assault on IS militants.

US President Barack Obama on Friday called Russia's dramatic foray into the conflict a "recipe for disaster" but pledged that Washington would not be drawn into a proxy war with Moscow in Syria.

Putin "doesn't distinguish between ISIL and a moderate Sunni opposition that wants to see Mr Assad go," Obama told reporters, using an alternative name for IS.

"From their perspective, they're all terrorists."





- Claims of civilian casualties -





Turkish President Recep Tayyip Erdogan, one of the fiercest critics of Assad, for his part urged Putin to reconsider his strategy in Syria.

"I will definitely speak to Putin," he told Al-Jazeera Arabic on Saturday.

"I want to understand why Russia is so interested in Syria," Erdogan said, adding he had "received information" that 65 people had died so far in Russian bombing runs, without specifying the source of the toll.

Putin has said Moscow's air strikes are pre-emptive, stressing the need to hunt down IS militants before they cross into Russia, which has a large Muslim population.

Its entry this week into the Syrian conflict is Russia's first major military engagement outside the former Soviet Union since the occupation of Afghanistan in 1979.

"Over the past 24 hours SU-34 and SU-24M jets of the Russian airborne formation in Syria made more than 20 sorties over nine Islamic State infrastructure facilities," the defence ministry said on Saturday.

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SU-34 fighters jet dropped a concrete busting BETAB-500 bomb on a command post in the area of IS stronghold Raqa, it said, releasing a video of the strike.

"A powerful explosion in the bunker means that it was also used by terrorists to store a large amount of ammunition," it said.

Russia said its jets also destroyed an ammunition warehouse near the city of Jisr al-Shughur and targeted a training camp belonging to the IS group near the town of Maaret al-Numan, both in Idlib province.





- 'Dozen jihadists killed' -





The Syrian Observatory for Human Rights said Saturday that Russian strikes "hit IS positions west of Raqa overnight and explosions were heard in the city".

Raqa has acted as the extremist group's de facto Syrian "capital" since 2013.

The Observatory, which relies on a network of sources on the ground for its information, said Russian jets had killed 12 jihadists in Raqa this week.

But raids ordered by Moscow have also hit areas controlled by moderate groups that are fighting Assad and even prompted a claim by US Senator John McCain that Russian jets had killed rebel soldiers trained and funded by the CIA.

Russia said its strikes this week had destroyed IS positions in northern Aleppo province, neighbouring Idlib province and in Hama in central Syria.

But several military sources and the Observatory said Russia had hit areas controlled by groups other than IS.

The Observatory also says Russian strikes had killed several civilians and wounded doctors in a raid on a hospital in Hama.





- 'Shoring up Assad' -





British Defence Secretary Michael Fallon said that just five percent of Russian strikes had targeted IS.

"The vast majority are not against IS at all," he told Saturday's edition of The Sun newspaper.

Russia was "shoring up Assad and perpetuating the suffering," Fallon added.

The Syrian conflict began as an uprising against Assad's rule in 2011 but has splintered into a multi-front civil war with government troops, moderate rebels, jihadists and Kurdish forces all vying for control.

More than 240,000 people have been killed, with four million more forced to flee the country.

A US-led coalition has been bombing IS positions in Syria since September 2014 but the extremists have still managed to take ground, including the ancient desert city of Palmyra, a UN world heritage site.