“There are no images of the site of the attack; just of some affected people. These people do not show outward symptoms of a CW (chemical weapon) attack. Definitely not mustard; definitely not a nerve agent,” wrote Jean Pascal Zanders, senior research fellow at the European Union Institute of Security Studies.

“There are far too many people, including non-medical staff, around the affected persons. Apart from a surgical mask, nobody wears any protective garment or gas masks. If there would have been a CW attack with one of the agents known (or believed) to be in Syria’s arsenal, then most of the people present would have been fatally or seriously contaminated.”

Two senior U.S. officials said they don’t believe the rebels used chemical weapons and suggested the government itself may have manufactured the incident to preserve the ability to use them in the future.

“The regime is using (the claims) as a pretext for their own possible use,” one of the officials said. “The opposition has no such weapons.”

But the Russian Foreign Ministry, citing information from Damascus, said rebels did use chemical weapons, causing deaths and injuries.