'More proof needed' on Syria sarin use, say US
4 June 2013 Last updated at 19:32 BST
The White House has said more proof is needed to verify the use of sarin in Syria.
The US is continuing its effort to gather evidence about the likely use of chemical weapons.
It comes as France's foreign minister announced that it has been used "several times and in a localised manner" in Syria's crisis.
Laurent Fabius did not specify where, when or by whom the agent was deployed.
White House spokesman Jay Carney said: "We need to expand the evidence we have."