Weapons sent to Syrian rebels may end up in the hands of the sort of extremists who killed Drummer Lee Rigby, Vladimir Putin warned as the G8 summit ended with a degree of international accord over the crisis.
The Russian president said many elements of the forces opposed to Bashar Assad's regime were "exactly the same" as those behind the brutal murder of the soldier on the streets of London.
The G8 leaders issued a joint statement over Syria at the end of the summit
He drew the stark parallel at the close of the two day summit which saw the leaders of the world's most powerful nations paper over their differences on Syria to agree a joint position.
In a joint statement which prime minister David Cameron said was "turning up the pace" towards ending the bloody conflict, the eight nations said a planned peace conference should be held "as soon as possible".
They said they were "committed to achieving a political solution to the crisis based on a vision for a united, inclusive and democratic Syria".
After resistance from Russia, the statement made no reference to the future of President Bashar Assad, saying only that a transitional government must be formed "by mutual consent" between the different sides of Syrian society.
But it did make clear that Syria's military and security forces will be allowed to remain intact following a transition of power - seen as a tacit encouragement to Assad's senior officers to launch a coup.
Mr Cameron said many former supporters of Assad knew "in their hearts" that he could not be the future.
Tensions over Syria dominated the G8 gathering, which took place in the wake of an announcement by US president Barack Obama that the US was ready to arm the rebels despite Moscow's opposition.
Mr Cameron said Assad had "blood on his hands" and insisted it was "unthinkable" the dictator could play any part in the nation's future.
He told reporters: "I think it is unthinkable that president Assad can play any part in the future government of his country. He has blood on his hands, he's used chemical weapons.
Identifying individuals on both sides to take forward the process "opens the way to a genuine transition to a genuine Syria free from Assad, free from terror," he said.
"That is what we have agreed to work towards and I think that is an important step forward."
Mr Cameron again insisted no decision had yet been made over arming the rebels and said lifting the EU arms embargo had been important to "send a message".
He faces stiff political opposition at Westminster to extending UK help to the rebels to include arms - an issue on which he has promised MPs a vote.
With a majority of voters also opposed according to recent polls, Mr Putin issued a stark warning about the potential impact
"Recently the British people suffered a huge loss. It was a tragedy next to his barracks on the streets of London. A violent assassination, a very brutal killing of a British serviceman.
"Clearly the opposition is not composed all of this but many of them are exactly the same as the ones who perpetrated the killing in London.
"If we equip these people, if we arm them what is going to control and verify who is going to have these weapons, including in Europe as well.
"So we call all our partners, before making this dangerous step, think about it very carefully."
Mr Putin insisted that he had not been isolated in the talks with the other seven leaders - claiming that some agreed with him that there was not yet proof the regime had used chemical weapons.
It was the discovery of what the US said was convincing evidence that led President Barack Obama to say Washington could arm the rebels.
"Not all G8 members take the view that chemical weapons were in fact used by the Syrian Army. Some actually agree with us that there is no proof," he said.
He went on: "We had disagreements that is true but I never felt lonely and Russia never was on its own in making a statement in regards of Syria."
The G8 leaders also confirmed that they are making almost 1.5 billion US dollars available in additional funding for humanitarian operations in Syria and its neighbouring countries.