The Syrian army said an airstrike late on Wednesday by the U.S.-led coalition hit poison gas supplies belonging to Islamic State, releasing a toxic substance that killed "hundreds," but the coalition denied carrying out raids in the area.

A statement by the army, flashed on Thursday by Syrian state TV, said the incident in the eastern Deir al-Zor province proved that Islamic State and al-Qaida-linked militants "possess chemical weapons."

The report could not immediately be independently verified.