The Islamic State (ISIS/ISIL) has recently used chemical weapons in Iraq and Syria, two independent U.K.-based organizations have learned.

Conflict Armament Research (CAR) and Sahan Research, the two U.K.-based groups, “Sent teams to investigate allegations that ISIS used chemical munitions on three occasions last month. Two of the incidents occurred in Hasakah province in northern Syria, where ISIS is locked in battle with the Kurdish YPG group. The third involved a 120 mm mortar that landed near Kurdish positions at the Mosul Dam in northern Iraq but failed to explode,” reports CNN.

“The findings build on previous reporting that ISIS (the Islamic State in Iraq and Syria) has begun to adapt both suicide bombs and improvised explosive devices (IEDs) to include chlorine and other chemicals and may seek to exploit the use of chemicals as it develops new weapons,” it adds.

James Bevan, executive director of CAR, reportedly said that a dark yellow liquid emitting a powerful odor was still leaking from a mortar found on the scene of the Mosul Dam attack a week after it occurred.

“The investigation team also experienced headaches and nausea when in close proximity to the projectile/agent,” noted Bevan, describing symptoms consistent with exposure to a chlorine chemical agent, according to CNN.

CAR and Sahan Research also looked into ammunition that was launched into Tel Brak and Hasakah in northern Syria.

On June 28, ISIS had “fired a whole range of projectiles at a Kurdish YPG unit outpost” that had caused “loss of focus; loss of consciousness in some cases; pain from the waist down, resulting in temporary, localized paralysis,” and other problems, reportedly said Bevan.

“Nine days later, when researchers examined fragments of munitions at Tel Brak, they were covered in a chemical residue which still had an acrid odor and caused powerful throat and eye irritation,” reports CNN. “At a hospital in Qamishli, several of the affected fighters tested positive for PH3, a phosphine-based chemical used as an insecticide or fumigating compound.”

A rocket containing a chemical liquid reportedly struck a home in Hasakah on the same day as the Tel Brak attack.

“The projectile had been fired from a village about four kilometers away which was then under the control of ISIS, Bevan said,” according to CNN. “Again, investigating teams found residues that ‘emitted an acrid odor and induced powerful throat and eye irritation.’”

CAR teams have reportedly been operating in both Iraq and Syria for a year, recording tens of thousands of weapons and munition types used by ISIS.

ISIS is experimenting with different designs, said Bevan.

“We consider this very much a test run, using improvised munitions and filling them with chemicals that are available to them,” Bevan told CNN.

“If they deem this to be militarily effective, then we have suspicion that they will use them again,” he added.