A report made by chemical weapons watchdog the Organization for the Prohibition of Chemical Weapons (OPCW) revealed Tuesday that the group had determined "with a high degree of confidence" that chlorine gas was used to attack three rebel-held Syrian villages last year.

The investigators relayed witness reports of falling barrel bombs which released the toxic chemicals, affecting between 350 and 500 people and killing 13. Chlorine gas is not listed as a chemical weapon, and is used for industrial purposes around the world. It can, however, be used as a weapon to induce respiratory irritation.

One village investigated for the OPCW report, Kafr Zita in the north of the country, was said to have been targeted by hundreds of attacks with conventional weapons and hit with toxic chemicals 17 times between April and August 2014.

Security council split

The UN Security Council, which discussed the report on Tuesday, has been heavily involved in the issue of chemical weapon use in the Syrian civil war, following an August 2013 sarin gas attack that the US says killed more than 1,400 people.

Following the incident, the Security Council unanimously adopted a resolution ordering Syria's chemical weapons stockpile to be destroyed. Some 1,300 metric tons of weapons were then removed from the country.

Diplomats told news agency AFP that Tuesday's closed-door discussion prompted a clash between Security Council members Britain, France, and the United States, who voiced concern over the findings, and Russia, Syria's most valuable ally.

The Syrian regime "must be shown it is not enough to destroyed declared CW (chemical weapons); must stop dropping chemical-laden explosives on civilians," tweeted US Ambassador to the UN Samantha Power, despite the fact that the report did not assign blame for the attacks.

Power, argued, however, that witness statements in the report regarding the use of helicopters point to the government of Bashar al-Assad, as none of the rebel groups have aircraft. The Syrian government has repeatedly blamed "terrorists" for the gas attacks.

The ongoing conflict in Syria has claimed more than 200,000 lives and displaced a third of the country's population in four years.

es/bk (AP, AFP)