The Organization for the Prohibition of Chemical Weapons (OPCW) has suggested sulphur mustard gas or similar toxic chemicals could have been used in Iraq.
Conducted after nearly 35 Kurdish troops fell ill while fighting ISIS in Iraq last August, laboratory tests have suggested prohibited sulphur mustard gas had been used in the country, reported Reuters.
However, the OPCW has not disclosed the names of any organisation or agents behind the use of the banned chemical weapons.
In January, a report from the organisation suggested that Syrian civilians could have been exposed to Sarin gas, after 11 incidents of the use of toxic chemicals were investigated.
The OPCW fact-finding mission determined mustard gas and chlorine had been used in thickly populated civilian localities in Syria.
According to Amnesty International, hundreds of civilians have been killed in chemical weapons attacks since the start of the Syrian crisis four years ago.
International humanitarian law prohibits the use of chemical weapons.
Earlier in 2013, Syria agreed to terminate its chemical weapons programme after hundreds of people were killed in a Sarin gas attack in Damascus.
Following the decision, OPCW collaborated with the UN Security Council (UNSC) to identify those responsible for the attack, as well as dispose of numerous hydrogen fluoride cylinders at its facility in Texas, US.