Footage obtained by ITV News raises further questions about an alleged chemical attack in the suburb of Zamalka in the rebel-held area of the capital Damascus in August.
It shows rebel fighters who have seized a pharmaceuticals factory from the Assad regime which they claim Government forces occupied to stop medicine getting to civilians.
The medicines include the drug atropine, which can be used as an antidote for the deadly nerve gas Sarin.
One rebel said: "We found atropine injections which we needed to back on the 21st August when the chemical attack happened in Zamalka 4km away from here
ITV News' Middle East Correspondent Geraint Vincent reports:
The rebels also revealed the network of tunnels used to avoid and attack President Assad's army.
One rebel fighter described how they were used to go "under the Assad army and push up behind him".
Some rebels suggest the August chemical attack launched in the Zamalka in the rebel-held area of the capital Damascus, was in response to the effectiveness of their tunnel attacks.