A report in The Guardian has revealed western powers ignored a Russian offer to help depose Syria's president, Bashar al-Assad three years ago.
Former Finnish president and Nobel peace prize laureate Martti Ahtisaari - a senior negotiator involved in back-channel discussions at the time - said Assad could have stepped down as part of a peace deal.
Since the offer was made in 2012, tens of thousands of people have been killed and millions uprooted, causing the world's gravest refugee crisis since the second world war.
Ahtisaari held talks with envoys from the five permanent members of the UN security council in February 2012. He said that during those discussions, the Russian ambassador, Vitaly Churkin, laid out a three-point plan, which included a proposal for Assad to cede power at some point after peace talks had started between the regime and the opposition.
But he said that the US, Britain and France were so convinced that the Syrian dictator was about to fall, they ignored the proposal.
"It was an opportunity lost in 2012," Ahtisaari said in an interview.
Russian support for Assad
Officially, Russia has staunchly backed Assad through the four-and-half-year Syrian war, insisting that his removal cannot be part of any peace settlement. Assad has said that Russia will never abandon him. Moscow has recently begun sending troops, tanks and aircraft in an effort to stabilise the Assad regime and fight Islamic State extremists.
A second report in The Guardian says a large convoy of Russian vehicles was reportedly on the move through central Syria on Wednesday, sparking new claims that renewed Russian support for the ailing Assad regime could lead to Moscow effectively running the war.