The Mil Mi-25 Hind gunship (capable to carry rockets that can theoretically be loaded with chemical agents) can be clearly seen releasing bombs leaving fanning smoke trails. Although the resemble flares, these are actually ZAB submunitions igniting upon dispersal, and falling near Deir ez-Zour.
Such subminutions are contained into RBK-250 cluster bombs.
According to the Rogue Adventurer blog, RBK-250 ZAB-2.5 (Zazhigatelnaya Aviatsionnaya Bomba; incendiary aircraft bomb) 250-kg cluster bomb contains 48 submunitions in total in three different variations: one with an incendiary (thermite) composition, one with a thermite + high explosive composition, and one with a thermite + jellied incendiary composition.
H/T Bjørn Holst Jespersen for the help in identifying the bomblets