The World Health Organization (WHO) requires "unhindered access" to the Duma city in Syria to check the reports of its partners that 500 people have been affected by the chemical attack.
The Syrian government denies being behind this attack.
At least 70 people died as a result of chemotac in Syria - doctors
Why is war in Syria?
The United States threatens that their response to a chemical attack will be "tough", while Russia called it "an occasion" for an attack on its ally - the authorities of Syria.
Council of the UN: Russia vetoed the US resolution on Syria
According to sources of the WHO, as a result of the attack, more than 70 people died.
According to the organization, its healthcare partners reported that 500 people suffered from symptoms related to the effects of toxic chemicals: they had difficulty breathing, irritation of the mucous membranes and impaired central nervous system functioning.
"It is reported that two healthcare facilities have suffered from these attacks," the WHO statement said.
"WHO requires immediate unimpeded access to the area to help those who have suffered and assess the damage done to people's health ...", added there.