An unconscious Syrian child receives treatment at a hospital in Khan Sheikhun, a rebel-held town in the northwestern Syrian Idlib province, following a suspected toxic gas attack on April 4, 2017.

A suspected chemical attack killed at least 58 civilians including several children in rebel-held northwestern Syria, a monitor said, with the opposition accusing the government and demanding a UN investigation. / AFP PHOTO / Omar haj kadour        (Photo credit should read OMAR HAJ KADOUR/AFP/Getty Images)
Video shows gas attack aftermath
01:23 - Source: CNN

Editor’s Note: This article contains extremely graphic images of dead children. All times are local.

Nightmarish accounts continue to filter out of Khan Sheikhoun, the northern Syrian town still reeling from what is feared to be the deadliest chemical attack in the country in years.

Investigations are underway to determine who was responsible for the Tuesday morning attack that left at least 70 dead, according to activists.

This is how it unfolded, based on eyewitness accounts provided to CNN.