The symptoms of 500 Syrian patients treated after Saturday's attack on Douma point to the use of toxic chemicals, the World Health Organization (WHO) said, citing reports from its medical sources in the country.
"In particular, there were signs of severe irritation of mucous membranes, respiratory failure and disruption to central nervous systems of those exposed," the WHO said on Wednesday.
"WHO demands immediate unhindered access to the area to provide care to those affected," added the agency's emergency response chief, Peter Salama.
The UN health agency in Geneva issued its statement as the Organization for the Prohibition of Chemical Weapons (OPCW) was deploying investigators to Douma, the last remaining Damascus suburb held by rebels.
More than 70 people reportedly died during the attack, including 43 who apparently were killed by highly toxic chemicals, the WHO said.
Syria has previously denied that any such attack took place, while Russian officials called the allegations "fake news."
