'Growing evidence' of chemical weapons use in Syria - UK
26 April 2013 Last updated at 22:49 BST
There is "limited but growing" evidence that Syrian government troops have used chemical weapons, UK Prime Minister David Cameron says.
"It is extremely serious, this is a war crime," Mr Cameron told the BBC.
On Thursday, the White House said that US intelligence agencies believed "with varying degrees of confidence" that Syria had used the nerve agent sarin.
Gordon Corera reports.