Russia says its Syria airstrikes led 600 IS militants to flee to Europe

Russian airstrikes on Saturday targeting the Islamic State (IS) militants in Syria have sown "panic," forcing some 600 "militants" to abandon their positions and head to Europe, Moscow claimed.

"Our intelligence shows that militants are leaving areas under their control. Panic and desertion have started in their ranks," Colonel General Andrei Kartapolov, a senior official with the Russian General Staff, said in a statement.

"Some 600 mercenaries have abandoned their positions and are trying to find their way into Europe," he added.

Meanwhile in London, Britain's Prime Minister David Cameron on Saturday accused Moscow of backing "butcher" Syrian President Bashar al-Assad with its airstrikes, which he said were often not aimed at IS.

Cameron said Russian forces were "making the situation worse" as they pressed a bombing campaign in the IS stronghold for a fourth day. 

His comments came as British intelligence forces observed that only one in 20 Russian air strikes were hitting IS targets, according to Britain's defence minister.

"It's absolutely clear that Russia is not discriminating between ISIL [Islamic State] and the legitimate Syrian opposition groups and, as a result, they are actually backing the butcher Assad and helping him and really making the situation worse," said Cameron.

"They have been condemned across the Arab world for what they have done, and I think the Arab world is right about that."

The British prime minister added: "We should be using this moment now to try to force forward a comprehensive plan to bring political transition ... because that is the answer for bringing peace to the region."

Cameron's comments, delivered ahead of his Conservative Party's annual conference in Manchester, northern England, echo those of his defence minister, Michael Fallon, published Saturday in the Sun newspaper

British intelligence services observed that only five percent of Russian air strikes had attacked the IS group, with most "killing civilians" and Free Syrian forces fighting Assad, Fallon told the tabloid.

He said that Russia's intervention had further "complicated" the crisis, while suggesting that Britain should extend its own bombing campaign - currently only operational against IS in Iraq - to Syria.

"We're analysing where the strikes are going every morning," he told the paper. "The vast majority are not against IS at all."

The United States has also accused the Kremlin of trying to buttress Assad, with President Barack Obama describing the airstrikes that began on Wednesday as "a recipe for disaster".

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

"From their perspective, they're all terrorists. And that's a recipe for disaster."

The American president said he had made it clear to Putin during their meeting in New York earlier this week that it's not possible to "rehabilitate" Assad in the eyes of Syrians.

"This is not a judgment I'm making," he added. "It is a judgment that the overwhelming majority of Syrians make."

Obama also noted that he would not join the Russian military campaign as Moscow acts in a way to support Assad rather than going after IS.

"The Russian policy is driving those folks [rebels] underground, or creating a situation in which they are de-capacitated, and it's only strengthening ISIL." he said.

Obama said the US wanted the trained Syrian fighters to focus on IS, while these forces were also bombed by the Syrian government.