The Russian President, Vladimir Putin, rounded on Britain on Sunday, accusing David Cameron of betraying humanitarian values by supporting Syrian rebels with “blood on their hands”.

In harsh and undiplomatic language, Mr Putin accused the UK and other Western powers of attempting to arm rebels who “kill their enemies and eat their organs”. He insisted that Russia would continue to arm what he said was the recognised “legitimate government” in Syria and called on other countries to respect the same rules.

Mr Putin’s comments, ahead of Monday’s G8 summit in Northern Ireland, suggest that earlier British hopes of a softening of Russia’s position on Syria were misplaced. After around an hour of bilateral talks with David Cameron in Downing Street, Mr Putin’s spokesman told The Independent that the two sides remained as far apart as ever.

Download the new Independent Premium app Sharing the full story, not just the headlines

“There are very serious disagreements in terms of who is guilty and who is to blame,” he said. Asked what the impact of the American decision to arm Syrian rebels would be on potential peace talks, he added: “It makes it harder.”

On Monday, Foreign Secretary William Hague backed Mr Cameron's assessment, saying that the UK had to save the Syrian rebels from being "exterminated." But elsewhere in the Tory Party, London Mayor Boris Johnson warned that there could be no guarantee that weapons sent to moderate rebels wouldn't end up in the hands of "odious, twisted, hate-filled thugs."

In a press conference after the talks yesterday, Mr Cameron admitted that “President Putin and I have our disagreements on some of the issues”, but insisted the G8 could bring “new momentum and leadership” to start negotiations in Syria.

“What I take from our conversation today is that we can overcome differences if we recognise that we share some fundamental aims: to end the conflict, to stop Syria breaking apart, to let the Syrian people choose who governs them and to take the fight to the extremists,” he said.

“If we leave Syria to be fought over between a murderous dictator and violent extremists we will all pay the price,” he added.

But when Mr Putin was asked by British journalists about comments by Mr Cameron last year – that those supporting President Assad had the blood of Syrian children on their hands – he reacted angrily. He said: “One does not need to support people who not only kill their enemies, but open up their bodies, eat their intestines in front of the public and cameras. Are these the people you want to support?

“Is it them you want to supply with weapons? Then this probably has little relation to humanitarian values that have been preached in Europe for hundreds of years.”

Inside Politics newsletter The latest news on Brexit, politics and beyond direct to your inbox Enter your email address Continue Continue Please enter an email address Email address is invalid Fill out this field Email address is invalid Email already exists. Log in to update your newsletter preferences Register with your social account or click here to log in I would like to receive updates on politics every morning by email Update newsletter preferences

Mr Putin was referring to video footage on the internet of one rebel fighter eating what appeared to be the heart of a government soldier.

Downing Street sources said the talks had gone better than the press conference suggested.

Mr Cameron denied that Britain wanted to arm extremists within the Syrian opposition and defended the lifting of the EU arms embargo on supplying weapons to the rebels.

“We, rightly, changed the terms of the EU arms embargo because it was almost saying there was some sort of equivalence between Assad on the one hand and the official Syrian opposition on the other,” he said.

“The Syrian opposition have committed to a democratic, pluralistic Syria that will respect minorities, including Christians.”

In an interview with the BBC last night, Mr Cameron went further and said that Western powers needed to arm the rebels precisely to prevent the opposition being dominated by extremists.

“If we don’t work with the Syrian opposition then we shouldn’t be surprised when the only parts of the Syrian opposition that are proving effective are the most extreme and the most dangerous,” he said.

“I want to avoid that. One of the things I hope I will be able to agree with President Putin – although we come at this from a different angle – is that we’ll all be better off if we can expel al-Qa’ida extremists from Syria.”

But ahead of Monday’s G8 summit, Mr Cameron appears increasingly isolated domestically over his enthusiasm for greater British involvement in Syria.

At least five cabinet ministers have expressed their private opposition to the plan, while a significant number of Conservative and Liberal Democrat MPs have indicated that they would be prepared to vote against the Government if it is put to a vote in the House of Commons.

Nick Clegg stressed on Sunday that no UK decision on arming the rebels appeared imminent. The Deputy Prime Minister told the BBC’s Andrew Marr Show: “At this point we’re not providing arms. If we wanted to, we would do it. We clearly don’t think it is the right thing to do now or else we would have decided to do it.”

Describing the provision of non-lethal equipment, which is the current strategy, Mr Clegg insisted it was possible for the UK to take a different position from that of the Americans.

“We need to work in concert with our allies but we do not need to do the identical thing,” he said.

Other senior figures called on Mr Cameron to stay out of the conflict. The Conservative MP Julian Lewis warned against Britain getting involved in the “snakepit” of the Syrian conflict, and predicted the Prime Minister would struggle to get MPs to agree to arm the rebels.

“I have little doubt that the Prime Minister would struggle to get this approved by Parliament because so many of us think it’s not in the British national interest to get involved with this snakepit,” he said.

The former head of the Army, Lord Dannatt, also cautioned that supplying arms to the Syrian opposition could turn into a “much larger intervention”.

He said: “I’m very much in the camp of those who would not wish to be involved and intervene in any shape or form.

“Goodness, if we’ve learned anything in the last few years, it is that we don’t get involved in another intervention without having a very clear idea of what we’re going to do, who we’re going to help, what the plan is, and what the exit strategy is. Surely we’ve not all forgotten those lessons of Iraq and Afghanistan so quickly?”