(CNN) ISIS recently used devices filled with chemical agents against Kurdish forces and civilians in both Iraq and Syria, a joint investigation by two independent organizations has found.

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.

The two U.K.-based groups -- Conflict Armament Research (CAR) and Sahan Research -- 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.

CAR said this was "the first documented use by (ISIS) forces of projectile-delivered chemical agents against Kurdish forces and civilian targets."

Evidence found

James Bevan, executive director of CAR, said the group's investigators went to the scene of the Mosul Dam attack a week after it occurred. Even then, the dark yellow liquid leaking from the mortar emitted a powerful odor. "The investigation team also experienced headaches and nausea when in close proximity to the projectile/agent," Bevan said, symptoms consistent with exposure to a chlorine chemical agent.

The device was sent for further testing by the Kurdish Regional Government. A senior official with the Kurdish Region Security Council told CNN Sunday that they expected to confirm the device contained chlorine. The official said there had been several other instances in which ISIS had used chlorine against Kurdish Peshmerga units, and the group's tactics were evolving.

CAR and Sahan Research also investigated the munitions that landed in northern Syria -- at Tel Brak and Hasakah. Bevan said ISIS forces had "fired a whole range of projectiles at a Kurdish YPG unit outpost" on June 28th. They had caused "loss of focus; loss of consciousness in some cases; pain from the waist down, resulting in temporary, localized paralysis" and other problems.

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. 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.

On the same day as the Tel Brak attack, a home in Hasakah was struck by a rocket that contained a chemical liquid whose residue was dark olive green. The projectile had been fired from a village about four kilometers away which was then under the control of ISIS, Bevan said. Again, investigating teams found residues that "emitted an acrid odor and induced powerful throat and eye irritation."

'A test run'

Malik Ellahi, spokesman for the Organization for the Prohibition of Chemical Weapons, told CNN that the OPCW had not seen the evidence collected by CAR but "any use of toxic chemicals as weapons constitutes use of chemical weapons which is clearly prohibited by the Chemical Weapons convention."

CAR has had teams operating in both Syria and Iraq for a year, documenting tens of thousands of weapons and ammunition types used by ISIS.

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Bevan says ISIS experiments with different designs. "We consider this very much a test run, using improvised munitions and filling them with chemicals that are available to them."

An agricultural chemical like phosphine would be available in farming regions of northern Syria.

ISIS often boasts through its official media outlets of its ingenuity in building and adapting weapons. Last month it released photographs of its fighters manufacturing frames for Katyusha rockets and of an IED workshop in Fallujah, near Baghdad, described by analysts Flashpoint Partners as the "epicenter of the group's explosive-making efforts, home to its manufacturing facilities for proprietary rockets" and other weapons.

Even though the attacks at Mosul Dam and Tel Brak were more than 200 kilometers (124 miles) apart, their similarities suggest that different ISIS commands are sharing technology and skills.

Past allegations

There have been a number of allegations in the past year that ISIS has used chlorine in attacks by suicide bombers and in IEDs in Iraq. CNN's Ben Wedeman reported that several members of the Iraqi security forces had been incapacitated last September by what appeared to have been chlorine gas released by an explosion near the town of Balad. ISIS had recently taken over a local water purification plant, where chlorine would likely have been present.

In March, the Kurdish Regional Government said residues tested by a laboratory in Europe had shown the use of chlorine during a suicide attack by ISIS at Eski Mosul on January 23. At the time, ISIS was trying to recapture an important road junction in the area and had sent a series of suicide bombs against Kurdish positions. A senior Kurdish security official said the vehicle had been laden with chlorine canisters. Several Peshmerga fighters were sickened in the attack.

There were also reports that ISIS used chlorine in roadside bombs set around Tikrit in March. ISIS was then trying to hold onto the town (unsuccessfully) in the face of a major Iraqi offensive. One video showed a large cloud of orange gas billowing into the air as an IED was set off in a controlled explosion.

Crude chlorine-based devices were also used by Iraqi insurgents against U.S. forces in 2006-07, often in combination with high explosives. In one attack in 2007, a suicide bomber detonated a truck of explosives and chlorine cylinders in Ramadi. Some 20 people were killed -- apparently by the explosion -- while scores more needed hospital treatment for the effects of chlorine.

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In the current conflict in Syria, the regime of Syrian President Bashar al-Assad has been repeatedly accused of using chlorine in bombs. The Syrian American Medical Society, which runs medical facilities in the country, documented 31 attacks using chlorine dropped from helicopters and over a three-month period this year. The Syrian government denies it has used chlorine bombs.

Bevan says the latest evidence of ISIS using chemicals is disturbing because it shows the group has access to chemical agents which can be weaponized and that it continues to experiment with munitions and delivery systems.

"If they deem this to be militarily effective, then we have suspicion that they will use them again," Bevan told CNN.