The White House has said it is "highly likely" that it is President Bashar al-Assad's regime, not rebels, behind any chemical weapons use.
Earlier, a leading member of the Independent International Commission of Inquiry on Syria, told Swiss TV statements from victims of the conflict suggested rebels had used the nerve agent Sarin.
Carla Del Ponte said that there was "strong, concrete suspicions but not yet incontrovertible proof".
However, she did not rule out the possibility that they might also have been used by government forces.
More top news
A large shipment of cocaine has been seized from a boat intercepted at sea by the Royal Navy and Coastguard.
World Superbike champion and TV presenter joined thousands of other bikers at an event to raise money for the Midlands Air Ambulance.
Spring takes a hike - for the time being