The White House said on Tuesday there was no evidence of claims by the Syrian government that the rebels had used chemical weapons, dpa reports.
"We are deeply sceptical of a regime that has lost all credibility," spokesman Jay Carney said. "And we would also warn the regime against making these kinds of charges as any kind of pretext or cover for its use of chemical weapons."
Carney said however that the United States was "looking carefully" at such claims, stressing that President Barack Obama remains concerned that Bashar al-Assad's regime could use chemical weapons as it becomes more beleaguered.