The World Health Organisation (WHO) on Wednesday (April 11th) demanded "immediate" access to the victims of an alleged chemical attack in Syria, where victims suffered symptoms consistent with exposure to toxic substances, AFP reported.

"We should all be outraged at these horrific reports and images from Douma" where Saturday's attack took place, said Peter Salama, the UN agency's chief of emergency response.

"WHO demands immediate unhindered access to the area to provide care to those affected, to assess the health impacts, and to deliver a comprehensive public health response," he added.

Citing information previously released by local health organisations, WHO said "an estimated 500 patients presented to health facilities exhibiting signs and symptoms consistent with exposure to toxic chemicals".

"There were signs of severe irritation of mucous membranes, respiratory failure and disruption to central nervous systems of those exposed," the statement added.

WHO has delivered medicine capable of treating certain types of chemical agents to clinics through a series of humanitarian convoys deployed across the country in recent years.