Rebel militia have reportedly shelled Government-held positions in Aleppo with poison gas munitions, injuring at least 28 soldiers, according to local media reports.
Both sides of the conflict have been accused of using chemical weapons at different timepoints during the long-running civil war in Syria.
It is not immediately clear what compound has been used in this instance, but chlorine and white phosphorus are known to have been weaponized and used offensively before. Chlorine gas causes severe irritation of the respiratory system, and may induce death at high concentrations. White phosphorus tends to stick to human skin and causes deep chemical burns.