Syrian opposition campaigners say Syrian forces fired chemical weapons at rebels surrounding an army base in the town of Adra near Damascus, killing two fighters and wounding 23.
"Doctors are describing the chemical weapon used as phosphorus that hits the nervous system and causes imbalance and loss of consciousness," said Mohammad al-Doumani, an activist in the nearby town of Douma, where the wounded were transported.
"The two fighters were very close to where the rockets exploded and they died swiftly. The rest are being treated with Atropine."
There was no independent confirmation of the attack, which follows the death of 26 people in a rocket attack near the city of Aleppo last week.
The authorities and rebels accused each other of firing a missile carrying chemicals there.