The Obama Administration has alleged that Syria's Assad regime resumed shelling at the site of the reported chemical attack, soon after a team of UN investigators, gathering evidence from the site, returned.
"The United Nations' team caravan was attacked en route to the site, and upon its return from its first day of work from the site, the neighbourhood was again bombarded and shelled, in a further indication of the utter lack of credibility of the Syrian regime on this matter," the White House Press Secretary, Jay Carney, told reporters on Sunday at his daily press briefing.
"We do not believe that credibility is going to be restored suddenly," he said. Carney said there is very little doubt that the Assad regime used those weapons because they have maintained control of the stockpile of chemical weapons in Syria.
Syria resumed shelling at site of chemical weapons attack: White House
"They alone have the capacity to use rockets to deliver chemical weapons. And they have continued prior to the use of chemical weapons, tried to clear that neighbourhood and have continued to shell that neighbourhood in the aftermath of the use of chemical weapons," he said.
Emphasising that the attack and the ensuing response would be a response to the violation of an established international norm, he said that "it is profoundly in the interest of the United States and of the international community that that violation of an international norm be responded to."
In response to a question regarding proof about the use of chemical weapons, he said, "We have seen the horrific results of the use of chemical weapons. We have seen it with our own eyes. And the evidence that chemical weapons were used is undeniable." "The proof comes from sources well beyond the US government, open sources, international organisations, witnesses on the ground."