APA reports quoting Al Arabiya that the activists at the Syrian Revolutionary Command Council said regime fighter planes were flying over the area after the bombardment, accusing the forces loyal to President Bashar al-Assad of using chemical agents.
The attack was on rebel-held areas of eastern Damascus.
According to Reuters news agency, the reported use of the chemical agents could not be immediately verified. The news coincides with a visit to Damascus by a United Nations team of chemical weapons experts. Bayan Baker, a nurse at Douma Emergency Collection facility, said the death toll from the attack, collated from medical centers in the region, was 213.
There was no immediate comment from Syrian authorities, who have denied using chemical weapons during the country's two-year conflict, and have accused rebels of using them, which the rebels deny.