State-run Syrian media posted images of the attack the government said killed 25 people and injured more than 110, CNN reported Wednesday.
However, the photos don't show a scene that is consistent with a chemical weapons attack, contends Jean Pascal Zanders, a senior research fellow at the European Union Institute of Security Studies.
Zanders said the images don't show the site of the attack, only "affected people" who do not show outward symptoms of a chemical weapons attack.
"There are far too many people, including non-medical staff, around the affected persons," Zanders said. "Apart from a surgical mask, nobody wears any protective garment or gas masks."
Two senior U.S. officials suggested the Syrian government may have manufactured the account as a way of justifying the use of chemical weapons in the future.
The Russian Foreign Ministry stood by the Syrian regime's claims, calling the incident "an extremely alarming and dangerous development."
Russian officials said they were worried about chemical weapons falling into the hands of "militants."
Syria, where President Assad Bashar's government has fought a two-year civil war, could have one of the world's largest stockpiles of chemical weapons, military analysts say.