( CNN) Horrifying images and video depict civilians — including children — struggling to breathe, foam coming from their mouths as they appear to die of asphyxiation after an airstrike on a rebel-held town in northwestern Syria on Tuesday.

Syria’s military has denied use chemical weapons and blamed rebels for the carnage, but activists say the regime is responsible for a compound strike which killed at least 70 people. Russia, meanwhile, has blamed the deaths on a Syrian airstrike on a “terrorist” ammunition depot.