The Kurdish administration in Iraq has accused the Islamic State (Isis) of using weaponised chlorine gas against Peshmerga forces.
The claim, which is bound to add a new dimension to the conflict, has been made by the Security Council of the semi-autonomous Kurdish government.
"The analysis, which was carried out at an EU certified laboratory, found the samples contained levels of chlorine that suggested the substance was used in weaponised form," an official statement on Twitter said.
The laboratory has not been identified by Kurdish officials and the claim is yet to be independently confirmed.
Samples from soil and clothes were said to have been taken after a car bomb attack on 23 January along the highway between the IS-stronghold of Mosul and the Syrian border. A truck loaded with "20 gas canisters" was found in the highway, the Kurdish statement added.
A Kurdish security source told Reuters that several Peshmerga fighters complained of vomiting, dizziness and nausea – which could be attributed to a chlorine gas attack - just after the suicide bombing incident.
The use of chemical weapons goes back to the World War and it has been strictly prohibited in war zones under the UN's 1977 Chemical Weapons Convention.
The US has said it is aware of the latest claims and expressed serious concern over the escalation.
"We find such allegations deeply disturbing, and if there are parties engaged in such use, they should be held appropriately accountable," Alistair Baskey, a spokesperson for the White House's National Security Council, said.
Earlier also it was alleged that IS had used chlorine gas in the intensifying conflict after the Islamist militants reportedly seized old but potent chemical weapons from Iraqi army bases when they overran the territories.