Iraqi Kurds claim to have evidence that Isis used chemical weapons against their fighters in January this year.
The Security Council of the semi-autonomous Kurdish region in northern Iraq say that soil and clothing samples, taken after an Isis car bomb attack on 23 January, are consistent with the use of chlorine gas.
Laboratory analysis showed that “the samples contained levels of chlorine that suggested the substance was used in weaponised form”. The allegations have not been independently verified.
The car bombing allegedly occurred on a main road between Mosul and the Syrian border.
A bomb was fired at the car by Kurdish forces to ensure there were no casualties, according to a security source.
Despite this precaution, about a dozen Kurdish fighters apparently experienced symptoms of nausea, vomiting, dizziness or weakness.
The samples, tested at an unnamed laboratory, were described as “leftovers from the suicide bomber”.
In a statement, the White House said that it could not confirm the allegations, but found them “deeply disturbing” and it was monitoring the situation “very closely”.
The use of chlorine as a weapon showed “growing desperation due to the pressure being applied by coalition air power and Iraqi ground forces”, a US defence official said.
The use of chlorine, a choking agent that dates back to the First World War, is banned under the 1997 Chemical Weapons Convention, which prohibits the use of toxic agents in warfare.
Chlorine has been used “systematically” in the ongoing civil war in neighbouring Syria, the organisation for the prohibition of chemical weapons, found last year.
Peter Sawcazak, a spokesman for the Dutch-based organisation, said: “We have not had a request from Iraq to investigate claims of use of chemical weapons in Iraq, and the OPCW cannot immediately verify the claims.”
The group would have to test its own samples before it could confirm the use of chemical weapons inside a member state.
Iraqi Kurds were victims of the deadliest chemical attack in recent history when Saddam Hussein’s air force bombed the town of Halabja, where at least 5,000 people were gassed to death.