Isis are using ‘significant quantities’ of US-made weapons to spread their reign of terror across the Middle East, according to a new report.

This finding came from London-based research group Conflict Armament Research (CAR) after it conducted on-the-ground investigations in Iraq and Syria.

It’s been known for a while that Isis has been using U.S military hardware, but CAR’s study is the first by a non-government body to try and document in detail what hardware the terrorist group, also known as the Islamic State (IS), is deploying.

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U.S weapons: An investigation by a London-based research team has found that Isis is using large quantities of American-made arms. Pictured is an Isis fighter holds a flag and a weapon in Mosul, Iraq, in June

Hardware: An American-made M16A4 assault rifle that CAR documented in the Middle East after it was recovered from Isis forces

Logistics: CAR noted that Isis appears to have a very well-organised supply system as weapons had been transferred with speed across large distances

CAR’s report said: ‘Islamic State forces have captured significant quantities of US-manufactured small arms and have employed them on the battlefield.’

The Kurdish People's Protection Units (YPG) and the Kurdish Regional Government Peshmerga Forces in Iraq habitually use recovered Isis weaponry to supplement their firepower, but CAR said it documented U.S weapons just two days after their capture, so they could be easily differentiated.

Small arms being used by Isis include American M16A4 assault rifles and XM15-E2S semi-automatic rifles.

CAR also noted that Isis appears to have a very well-organised supply system as weapons had been transferred with speed across large distances.

It said: ‘YPG forces captured US-made material documented close to Ayn al-Arab, Syria, roughly two weeks after the fall of Mosul to IS forces.

‘The distance between the two regions is roughly 500 km. The speed of transfer to Ayn al-Arab demonstrates the logistical competence of IS forces and the strategic importance of Ayn al-Arab to the group.’

Worrying: M79 90mm anti-tank rockets captured from IS forces in Syria

Brutal: A Chinese PKM-pattern M80 machine gun that was being used by Isis

Forbidding: These photographs show how Isis has acquired some powerful equipment

Small arms being used by Isis include American M16A4 assault rifles and XM15 semi-automatic rifles

Other weapons Isis is using include M79 90mm anti-tank rockets given to the Free Syrian Army by Saudi Arabia, Chinese-made M80 general-purpose machine guns and a Croatian Elmech sniper rifle.

CAR noted that the origin of many weapons was disguised by an unknown party using used oxy-acetylene torches or arc-welders to remove the serial numbers.

CAR director James Bevan told MailOnline: ‘Excluding activities by state intelligence services, of which we know little and are not in the public domain, this is the first time anyone has sent a field investigation team to document captured IS weapons.’

The study's findings were revealed as news emerged that Britain has begun arming the Kurds to fight back against ISIS.

David Cameron told MPs, in a statement following last week’s Nato summit in Newport, that Britain ‘will continue to support the Kurds, including by providing them with arms and training their troops’.

Until now the Government has limited itself to transporting weapons from former Soviet countries to the Kurds, for example from Albania.