David Cameron said Britain has spent over £300 million and "saved tens of thousands of lives" in Syria.
The Prime Minister said: "I've been to Jordan and seen one of the refugee camps myself and I know how much money and how much effort is going in.
"Britain, as ever, is a world leader at helping those who need help, and the people of Syria are right up at the front of that right now."
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A mild night and another misty, grey start in places in the morning.
John Kelly said he was "broken hearted" by the criticism, adding the president had expressed his condolences "the best way that he could".
A survey by ITV News found Tory activists are surprisingly supportive of the Prime Minister, despite the result of the General Election.