Decades of irresponsible arms transfers to Iraq fuelled the Islamic State group's firepower and ability to carry out atrocities on a massive scale, an Amnesty International report says.
The London-based human rights watchdog is calling for tougher controls to put a stop to the alarming fallout from the proliferation of weapons in the country.
"The vast and varied weaponry being used by the armed group calling itself Islamic State is a textbook case of how reckless arms trading fuels atrocities on a massive scale," Amnesty researcher Patrick Wilcken said in a statement after the report was released on Tuesday.
"Poor regulation and lack of oversight of the immense arms flows into Iraq going back decades have given IS and other armed groups a bonanza of unprecedented access to firepower," he said.
The huge amounts of internationally manufactured weapons IS seized when it took Iraq's second city Mosul in June 2014 were used to take over other parts of the country and commit crimes against civilians, the report said.
Besides its massive haul in Mosul, the jihadist organisation also captured vast quantities of military equipment when it seized army and police bases in Fallujah, Tikrit, Saqlawiya, and Ramadi as well as in Syria.
As Iraq's security forces battle to recapture Ramadi, the capital of Anbar province, their task is complicated by IS' acquisition when it seized the city in May of what Amnesty said were "more than 100 armoured fighting vehicles, including dozens of tanks and armoured personnel carriers."
IS has disseminated these windfalls across its multiple fronts very effectively, with some weapons seized in Mosul in use barely two weeks later in an area of northern Syria some 500 kilometres away.
Amnesty inventoried the weapons IS is confirmed to possess and said the results "reflects decades of irresponsible arms transfers to Iraq".
While IS' staple remains Russian-designed weapons such as the Kalashnikov assault rifle, Amnesty found that the group has been using arms and ammunition from at least 25 countries.