David Cameron holds Syria humanitarian relief talks with G20 world leaders as international tensions continue over the crisis.
While world leaders fall out over the use of chemical weapons in Syria, the reality on the ground is that both sides in the conflict are engaged in bitter clashes that make the situation increasingly intractable, reports Sky's Stuart Ramsay.
British Prime Minister David Cameron has announced an additional £52m in aid to help the estimated two million refugees who have fled the civil war in Syria.
"This is a moral imperative. This is the big refugee crisis of our time. As the (UN) Secretary General has made clear, seven million people are in dire need and chemical weapons attacks have made this even more acute," he told them.
"A Syrian becomes a refugee every 15 seconds while we sit here at this conference. That is 5,000 fleeing their homes and becoming homeless while we are at this G20 summit."
Relations among world leaders have become heated over possible US military action against President Bashar al Assad's regime following a deadly chemical weapons attack on August 21.
The US and Russia have been unable to agree on a way forward and President Barack Obama said he had "hit a wall" with Mr Putin, who has warned the use of force without UN approval would be "aggression" and a violation of international law.
Russia, a staunch ally of Syria, also reportedly dismissed Britain as a "small island no one pays any attention to" as relations boiled over at the summit.
US Ambassador Samantha Power told a news conference in New York that Russia has held the UN Security Council "hostage" over Syria, and Mr Obama's administration did not expect that to end.
"Even in the wake of the flagrant shattering of the international norm against chemical weapons use, Russia continues to hold the council hostage and shirk its international responsibilities," she said.
"What we have learned, what the Syrian people have learned, is that the Security Council the world needs to deal with this crisis is not the Security Council we have."
The summit was tasked with fostering strong, sustainable growth through encouraging long-term investment among nations, but has been overshadowed by the Syria crisis.
Scientists at Porton Down, in Wiltshire, found further evidence on Thursday that deadly sarin gas was used in the Damascus attack.
But the discovery, alongside evidence from France and the US, is unlikely to cause Russia to change its position.
On Thursday, the Syrian government wrote to the US Congress urging its members not to support the use of military force.
The letter, seen by Sky News, urged Congress to "communicate with us through civilised dialogue rather than the language of fire and blood".
