The Prime Minister today announced millions of additional UK aid to help victims of the civil war in Syria.
Much of the £52 million set aside will go towards medical training and equipment for civilians targeted by chemical attacks.
The announcement came as the G20 summit in St Petersburg has seen divisions over the international response to the allegations of chemical weapons used by Syrian President Bashar al-Assad's regime.
Mr Cameron has also called for international action to secure humanitarian access to war zones.
After defeat in the House of Commons prevented the Government from preparing for military action alongside US President Barack Obama, Mr Cameron has pivoted his efforts towards persuading G20 leaders at this week's St Petersburg gathering to increase their humanitarian support efforts.
The Prime Minister was yesterday forced to deny he was being marginalised, following reports that a senior aide to Russian President Vladimir Putin, who is hosting the G20 meeting, had dismissed Britain as “just a small island: no-one pays any attention to them”.
While Mr Cameron has said he doesn't believe the aide said this, Downing Street has demanded “clarification” of the remarks, which were denied by the Russian President's chief spokesman Dmitry Peskov. Mr Peskov said the comments did not reflect Moscow's true view of the UK and the “positive dynamics” of relations between the two countries.
Britain's new aid contribution brings the total amount of UK funding for assistance in Syria and neighbouring countries to £400 million.
At a meeting Mr Cameron urged fellow world leaders to dig deep to fund a £1.9 billion shortfall in the United Nations appeals for Syria.
While he acknowledged the deep disagreements voiced when Syria was discussed at last night's official dinner, Mr Cameron said that action on aid would show that the G20 had “a very large message” of support for the people of the war-torn Middle Eastern state.
“This is a moral imperative,” Mr Cameron told the meeting, attended by ministers from Canada, Japan, Australia, Saudi Arabia and Turkey and a senior official in the Obama administration, as well as UN Secretary General Ban Ki-moon and the EU's Jose Manuel Barroso and Herman van Rompuy.
“This is the big refugee crisis of our time. As the Secretary General has made clear, seven million people are in dire need and chemical weapons attacks have made this even more acute.
“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.
“It is also a political imperative. It will help us build international support for action by showing that our response is not just military. At a summit where people have focused on potential divisions over Syria, I wanted to bring you together to identify key priorities about the action needed to send a strong message about our commitment to the Syrian people and the urgent priority to do more.”