Investigators find with ‘utmost confidence’ that mustard gas was used in

The report did not mention ISIS, as the fact-finding mission was not mandated to assign blame, but diplomatic sources said the chemical had been used in the clashes between ISIS and another rebel group taking place in the town at the time.

The Organisation for the Prohibition of Chemical Weapons on Friday confirmed with “utmost confidence” that mustard gas was used in August in Syria.

Doctors Without Borders (MSF) said it had treated four civilians from one family who were injured in the attack.

The group says that during the incident “at least two people were exposed to sulfur mustard, and that it is very likely that the effects of this chemical weapon resulted in the death of an infant”. This was after the U.S. threatened military action following a deadly sarin gas attack on a rebel-held suburb of Damascus that killed hundreds of people.

When Syria joined the OPCW in 2013 under pressure from the global community, it declared a 1,300-ton chemical weapon arsenal that has since been destroyed. The White House, when asked, did not say whether it believed that ISIS was able of creating its own chemical weapons or if it acquired mustard gas through Assad’s stockpile. “The Syrian government has not used and will never use chemical weapons”, said Bashar Jaafari, who is the Syrian Ambassador to the UN.

“It raises the major question of where the sulfur mustard came from”, one source said. “Either they gained the ability to make it themselves, or it may have come from an undeclared stockpile overtaken by IS”.

Sulphur mustard – commonly known as “mustard gas” although it is liquid at ambient temperature – is a powerful irritant and blistering agent which causes severe damage to the skin, eyes and respiratory system and internal organs.

In August, the Pentagon said the militant group was suspected of having used them in an attack on Kurdish fighters in northern Syria.

Allegations that the jihadist IS militants have been using chemical arms have been increasing in recent months in both Iraq and Syria.

Local media, including Syria’s official SANA news agency, reported in August that the Daesh Takfiri group had launched the attack.