Medecins Sans Frontieres says hospitals it supports in Syria treated about 3,600 patients with "neurotoxic symptoms", of whom 355 have died.
The UN says more than 100,000 people have been killed since the uprising against President Assad began more than two years ago.
- 01:15: 21 August (10:15 GMT 20 Aug): Facebook pages of Syrian opposition report heavy fighting in rebel-held districts of Ghouta, the agricultural belt in eastern Damascus
- 02:45: Opposition posts Facebook report of "chemical shelling" in Ein Tarma area of Ghouta
- 02:47: Second opposition report says chemical weapons used in Zamalka area of Ghouta
- Unverified video footage shows people being treated on pavements in the dark and in a makeshift hospital
- Reports say chemical weapons were used in Ghouta towns of Irbin, Jobar, Zamalka and Ein Tarma as well as in Muadhamiya to the west, but this is not confirmed
- Syrian government acknowledges military offensive in the Ghouta area but denies chemical weapons use