In an exclusive video interview with AFP news agency, he said "there was no order to make any attack".
More than 80 people were killed in the rebel-held town of Khan Sheikhoun on 4 April, and hundreds suffered symptoms consistent with a nerve agent.
Witnesses said they saw warplanes attack the town but Russia says a rebel depot of chemical munitions was hit.
Shocking footage showed victims - many of them children - convulsing and foaming at the mouth. Sufferers were taken to hospitals across the border in Turkey.
