I haven't seen this picked up anywhere else, but Reuters is reporting that a UN official says they have no evidence that the Syrian regime has used chemical weapons in its ongoing civil war:
U.N. human rights investigators have gathered testimony from casualties of Syria's civil war and medical staff indicating that rebel forces have used the nerve agent sarin, one of the lead investigators said on Sunday.
The United Nations independent commission of inquiry on Syria has not yet seen evidence of government forces having used chemical weapons, which are banned under international law, said commission member Carla Del Ponte.
I have no idea if this is reliable or not. However, for more on just how shaky the evidence is about the use of chemical weapons in Syria, you might try this Guardian piece from a few days ago. Overall, it suggests that the Obama administration might indeed be wise to collect more definitive evidence about this before they do anything rash.