Kurdish fighters and weapons experts say the Islamic State militant group has fired chemical weapons on Kurdish forces in Syria and Iraq.
Two Britain-based organizations investigating the attacks have released a joint statement saying Islamic State militants targeted Iraqi Kurdish fighters with a chemical agent on June 21 or 22.
A statement also described a similar attack on Kurdish positions in Syria's northeastern Hasakeh province on June 28.
Investigators said projectiles launched at the Kurds released a yellow gas that caused burning in the eyes, nose and throat, as well as headaches, muscle pain, impaired mobility, and vomiting after prolonged exposure.
Those exposed to the chemical were quickly given medical treatment and no one died.
Investigators also said Kurdish fighters have recently captured industrial-grade gas masks from Islamic State forces, indicating they are "prepared and equipped for chemical warfare."
The U.S. National Security Council, part of the Obama administration, has said it is aware of the reports and is monitoring the situation closely.
Kurdish fighters have played a vital role in the fight against the Islamic State group, which has seized territory in both Syria and Iraq, declaring a cross-border "caliphate" from which it claims to rule all Muslims.
The Kurds have been working in cooperation with U.S.-led airstrikes to regain some of that territory in northern Syria this year.