Inspectors have concluded that a "toxic chemical" containing chlorine was used in an attack last year in the Syrian town of Douma, at the time held by rebels but besieged by pro-regime forces, the global chemical weapons agency said on Friday. The attack on April 7 killed dozens of civilians and prompted air strikes against the regime of Bashar Assad by Britain, France and the United States. In a statement, the Organization for the Prohibition of Chemical Weapons (OPCW) said the mission visited Douma, analyzed samples taken from the scene and from people affected, interviewed witnesses and studied toxicological and ballistics analyses. The data, it said, provided "reasonable grounds that the use of a toxic chemical as a weapon" took place on April 7, 2018. "This toxic chemical contained reactive chlorine. The toxic chemical was likely molecular chlorine." The Fact Finding Missions mandate does not include laying blame for the attack. In December, UN Secretary-General Antonio Guterres urged Syria to resolve "gaps, inconsistencies and discrepancies" in its declaration of chemical weapons. The UN chief said in a letter to the Security Council that he is "deeply concerned about the continued use of toxic chemicals as weapons” in Syria.