MOHAMED AL-BAKOUR via Getty Images
The report found 33 chemical weapon attacks to date.
Anadolu Agency via Getty Images
A fact-finding mission has been launched to find who is responsible.
Abdalrhman Ismail / Reuters
The attack was the deadliest use of chemical weapons in Syria since 2013.
This is the second alleged chlorine attack in as many months.
A hospital spokesman says medics had recorded four deaths from gas poisoning and 55 injuries.