David Cameron has vowed to do more to help refugees from the Syrian civil war as he arrived in Russia for a G20 summit set to be dominated by tensions over US plans for military strikes against the regime of president Bashar Assad.
The Prime Minister risks being sidelined at the G20 gathering in St Petersburg after ruling out British involvement in any military action in the wake of his shock Commons defeat on Syria last week.
He is not expected to have a formal bilateral meeting with US president Barack Obama, who is leading the international drive for an armed response to Assad's apparent breach of the prohibition of the use of chemical weapons. But he made clear he backs Mr Obama in taking robust action against Assad and said he will do his best to persuade fellow leaders to help those affected by the violence.
The UK is expected to add to its £348 million contribution to the relief effort, but the UN has still received less than half the funding it is hoping for from the international community. Mr Cameron said: "We are facing the worst refugee crisis of this century and millions of lives are being destroyed inside in Syria by Assad and his regime.
"The world needs to do more to help the innocent victims of this conflict who dreamt of a democratic and peaceful future but who are now living a nightmare far from their homes and struggling to feed their families and keep them safe.
"I will be using the G20 to ensure their needs are heard and to ensure the international community responds. We must make more money available for aid agencies to help ease the suffering and we must put pressure on both sides in the conflict to improve access so aid workers can get to those who most need help."
Mr Obama has cleared the first hurdle to obtaining Congressional approval for a strike, as the influential Senate Foreign Affairs Committee backed the use of force by a margin of 10 to 7, moving the measure to a full Senate vote next week. The proposal allows the use of force for 60 days, with the possibility of a 30-day extension.
The president has said he is confident of receiving approval from Congress for "limited and proportionate" military action, which he said would not involve US troops putting "boots on the ground" in Syria. Assad had flouted a chemical weapons ban enshrined in treaties signed by governments representing 98% of the world's population, he said, adding: "I didn't set a red line. The world set a red line."
Speaking in Sweden as he travelled to St Petersburg, the US president said the credibility of the international community was "on the line" if it allowed Assad to act with impunity. He repeated his "high confidence" that the regime was to blame for the sarin gas attack on a suburb of Damascus on August 21 which the White House believes killed more than 1,400 people, including 400 children.
France's prime minister Jean-Marc Ayrault, rallying support for French involvement in military action, told the National Assembly in Paris there was no doubt the Syrian government was to blame and a failure to react would allow Assad to launch a similar attack. But Mr Putin said any evidence on culpability for the attack should be presented to the UN Security Council, where Russia has repeatedly blocked reprisals against Assad.