A new investigation has revealed that most of the advanced weaponry used by ISIS came from supplies the US and Saudi Arabia sent to the region.

The study released by the London based Conflict Armament Research (CAR), claims to be the most comprehensive to date.

The investigation concluded that the weapons supplied to opposition groups “significantly augmented the quantity and quality of weapons available to ISIS forces in numbers far beyond those that would have been available to the group through battlefield capture alone”,

It said that the US and Saudi Arabia “indirectly allowed the terrorists to obtain substantial quantities of anti-armour ammunition” including anti-tank guided weapons (ATGW) and rockets with tandem warheads.

The study took over a three and a half years to conduct and was funded by the European Union. Entitled “Weapons of the Islamic State,” the report claims to be “unquestionably the most comprehensive, verified study of the group’s weapons to date.”

Press TV reports: The possession of these arms by Daesh remains a threat to the US-led coalition forces still operating in Syria and Iraq, according to the study released Thursday by Conflict Armament Research (CAR), a UK-based organization that monitors the movement of conventional weapons.

The weapons included anti-tank rockets purchased by the US military that ended up in possession of ISIL within two months of leaving the factory, according to the study, which was funded by the European Union and German government.

Efforts by the US and other countries to supply weapons to militant groups “have significantly augmented the quantity and quality of weapons available to (ISIL) forces,” the report concluded.

The study examined 40,000 weapons and other items recovered from Daesh, during the past three years.

CAR researchers were unable to determine whether Daesh captured the weapons on the war zone or whether the militants sold or gave the arms to the terror group.

The report cites an ISIL propaganda video showing the terror group’s fighters with weapons captured last year from the so-called New Syrian Army, a coalition of militant groups battling the government forces of Syrian President Bashar Assad.

It has long been known that ISIL captured huge amounts of US weapons, including tanks and artillery, when the terror group swept into Syria and Iraq in 2014.

The White House ended a secretive CIA operation begun by the administration of then President Barack Obama in 2013 to arm anti-Assad militants.

The covert program arming anti-Assad militants is distinct from the Pentagon’s publicly acknowledged operation to arm the so-called Syrian Democratic Forces (SDF), a US-backed alliance of Kurdish and Arab forces fighting ISIL, but not Assad.

Saudi Arabia, which like the US strongly opposes the Syrian government, also supplies weapons to militant groups.

The new study raises questions about other sources for weapons.

The report said most of the weapons secretly sent to militants in Syria were purchased by the United States and Saudi Arabia from arms manufactured in Eastern Europe. It said the way the US government purchased the weapons raised troubling concerns about controlling arms sales.

The US-led coalition has been conducting airstrikes against what are said to be Daesh targets inside Syria since September 2014 without any authorization from the Damascus government or a UN mandate.

The military alliance has repeatedly been accused of targeting and killing civilians. It has also been largely incapable of achieving its declared goal of destroying Daesh.