Weapons experts believe they have identified at least four occasions on both sides of the Iraq-Syria border where Daesh suicide  group has used mustard agents, the Express quoted an official as saying.

The US believes the terror group has a base dedicated to manufacturing these weapons.

US officials say: "They're using mustard. We know they are."

Mustard gas is a chemical weapon which was first used during the First World War and was reported to have left victims disfigured, or slowly dying over up to four weeks.

It can be deployed through artillery shells, aerial bombs, rockets and from spraying from planes.

Source: MENA