Syria's Ambassador to the United Nations in Geneva Hussam Edin Aala rejected the accusation, saying, "Syria can not possibly be using chemical weapons because it very simply has none in its possession".
While the OPCW didn't lay the blame with any one party, it said in a report released Tuesday that interviews with witnesses, the collection of environmental samples and the symptoms that patients exhibited in the aftermath allowed it to conclude that chlorine was dropped from two cylinders on the Saraqib area on February 4, 2018.
"The FFM determined that chlorine was released from cylinders by mechanical impact in the Al Talil neighbourhood of Saraqib".
In addition, the OPCW said environmental samples had demonstrated the unusual presence of chlorine in the local environment. Patients at medical facilities shortly after the incident also showed signs and symptoms consistent with exposure to chlorine and other toxic chemicals. Western observers said the use of helicopters in the attack suggested Syrian government involvement since the opposition did not have access to helicopters.
At least eleven people were treated for breathing difficulties in the Syrian city on February 4, the so-called Syrian Observatory for Human Rights said at the time.
Following delays, the OPCW was allowed to access the Douma site where it gathered more than 100 environmental samples.
In response to persistent allegations of chemical weapon attacks in Syria, the OPCW Fact-Finding Mission (FFM) was set up in 2014 with an on-going mandate "to establish facts surrounding allegations of the use of toxic chemicals, reportedly chlorine, for hostile purposes in the Syrian Arab Republic".
The Organisation for the Prohibition of Chemical Weapons released details of a report into the chlorine use on Wednesday.
The FFM's report on the Saraqib incident has been shared with States Parties to the Chemical Weapons Convention.
"These chemicals were detected in previous sarin attacks, Khan Sheikhoun, East Ghouta and no doubt Douma", Bretton-Gordon said.
Syria and Russian Federation have accused Syrian volunteer rescue workers of staging the April 7 video footage at the behest of the United States and its allies.