Britain has directly accused the Assad regime of gassing hundreds of Syrian civilians amid warnings that UN investigators face a race against the clock to find proof.
ITV News has obtained exclusive independent pictures of the site of the alleged attack that appear to show a rocket shell close to the victims.
The distressing pictures show men, women and children lying dead on the street where they apparently fell, as ITV News correspondent Paul Davies reports:
Warning: Paul's report contains scenes of a distressing nature
Although America expressed "grave concern" at the claims of a mass atrocity and Russia finally ceded that an inspection was required near Damascus, UN investigators in the city were made to wait at least another day before access negotiations with the Syrian government can begin.
A Syrian opposition group has said it is "critical" inspectors reach the site of the alleged attack within 48 hours and pledged to ensure their safety.
Pre-empting the investigation's findings, though, Britain has said a chemical attack is the "only explanation" for the deaths of hundreds of Syrians near the capital on Wednesday.
– Foreign Secretary William Hague
We do believe that this is a chemical attack by the Assad regime on a large scale.
It is now 48 hours since the reports started to come in of what seems to have been a terrible atrocity near Damascus including the use of chemical weapons.
This is not something that a humane or civilised world can ignore.
World leaders, though, remain at stalemate, trading near-certain claims over video evidence with the absence of concrete proof.
And while the West accused Syrian President Bashar Assad of a cover-up by preventing the UN team from visiting the scene, Moscow said the rebels were impeding an investigation.
ITV News Middle East Correspondent Geraint Vincent reports on the diplomatic deadlock:
Warning: Geraint's report contains scenes of a distressing nature
The United Nations, meanwhile, released data showing that a million children were among refugees forced to flee Syria, calling it a "shameful milestone".