Syria has agreed to a United Nations investigation into last week’s alleged chemical weapons attack outside Damascus.
But a senior White House official dismissed the move as “too late to be credible,” saying the US has “very little doubt” President Bashar Assad’s forces used such weapons.
The hardening of the US position came as calls for military action grow.
In a sign the US may be a step closer to an armed response, naval forces have already been dispatched toward Syria’s coastal waters, although President Barack Obama has cautioned against a hasty decision.
With France, Britain, Israel and some US congressmen urging swift military action against Assad’s regime if the use of chemical agents is confirmed, the UN team’s conclusions could have a dramatic impact on the trajectory of the country’s civil war.