UN chemical weapons experts in Syria
UN chemical weapons experts in SyriaReuters

The Organization for the Prohibition of Chemical Weapons (OPCW), confirmed on Wednesday that chlorine gas was used in attacks in northern Syria this year, according to the BBC.

The OPCW, which is the international body seeking to implement global laws banning chemical weapons, said it had found "compelling confirmation" of the use of chlorine, in pure or mixed form.

The attacks took place earlier this year in villages where rebels have been fighting government forces, according to the organization, which has been overseeing efforts to destroy Syria's chemical weapons.

Activists in Syria said several months ago that over 100 people had been killed in a chlorine gas attack in the town of Talmenes in Idlib province, and the United Nations Security Council has called for an investigation into the alleged attack. Since then there were reports of other such attacks.

The latest OPCW report said a toxic chemical was used "systematically and repeatedly" in the villages of Talmanes, Al Tamanah and Kafr Zeta in northern Syria, according to the BBC.

The report concludes "with a high degree of confidence" that the chemical in question was chlorine gas.

It says this conclusion was based on a study of the symptoms of people who were exposed to the gas, their response to treatment, as well as descriptions of the properties and behavior of the gas.

An OPCW team tried to visit one of the villages, Kafr Zeta, in May to gather evidence, but had to turn back after its convoy was attacked, the report noted.

U.S. Secretary of State John Kerry has said that he has seen “raw data” indicating that the Syrian government has used chlorine gas as a chemical weapon in a “number of instances” in recent months.

Syria has emphatically denied that it carried out chlorine gas attacks against civilians.