Russia's military intervention in Syria is making the situation worse and helping to support the "butcher" president Bashar Assad, David Cameron has claimed.

The Prime Minister said that Vladimir Putin's forces were not discriminating between Islamic State (IS) - also known as Isil - and moderate opposition forces who have been engaged in a bloody civil war against Assad.

Mr Cameron said: "It's absolutely clear that Russia is not discriminating between Isil 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.

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

"But we should be using this moment now to try to force forward a comprehensive plan to bring political transition in Syria because that is the answer for bringing peace to the region."

The Prime Minister was speaking in Oxfordshire before travelling to Manchester for the Conservative Party conference.

His comments echo the outspoken criticism of Russia's intervention by Defence Secretary Michael Fallon, who said the "vast majority" of strikes since president Putin began the action had not been aimed at IS jihadists but were instead "killing civilians" and the Free Syrian forces rebelling against Assad's regime.

Mr Fallon acknowledged the Russian involvement had "complicated" the situation but indicated he still believed that Britain should extend its own bombing campaign to target IS in Syria.

In an interview with the Sun he said initial Ministry of Defence intelligence suggested only one in 20 Russian air strikes so far were on targets to damage IS.

He said: "We're analysing where the strikes are going every morning. The vast majority are not against IS at all.

"Our evidence indicates they are dropping unguided munitions in civilian areas, killing civilians, and they are dropping them against the Free Syrian forces fighting Assad.

"He's shoring up Assad and perpetuating the suffering."

Mr Fallon denied that Russia's involvement had left Europe and the US looking weak.

"I don't accept he has outmanoeuvred us. He has complicated the situation in Syria. But we're not powerless."

He indicated that the changed circumstances would not prevent the Government pressing ahead with making the case to extend the RAF's strikes against IS from Iraq into Syria.

It would be "morally wrong" not to target IS in Syria, he said, adding: "We can't leave it to French and Australian, American aircraft to keep our own British streets safe."