Islamic State militants are using some weapons that originally came from the United States, according to a new report from the human rights group Amnesty International.

The report, released Tuesday, provides a glimpse into how the Islamic State has stockpiled the weapons it is using to fight battles in Iraq and Syria and commit deadly terrorist acts worldwide.

Amnesty International found the Islamic State has amassed more than 100 kinds of weapons and ammunition from at least 25 countries, and most of its weapons were stolen from the Iraqi military. Amnesty reported a large number of these arms were obtained when the Islamic State captured Iraq’s second-largest city, Mosul, in June 2014 and looted military stockpiles there.

The Mosul haul, which Amnesty described as a “windfall,” included American-made weapons and military vehicles. The organization said both were subsequently used in Islamic State activities elsewhere in the country as the group successfully took control of additional territory.

The report comes days after President Barack Obama gave an address from the Oval Office and said one of America’s strategies to defeat the Islamic State terrorists was to continue providing training and support to local groups who were fighting the insurgents in the Middle East, rather than deploy large numbers of American soldiers there. But Amnesty’s report provides evidence that strategy seems to have, somewhat inadvertently, aided the Islamic State’s terror campaign.

“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,” Patrick Wilcken, a researcher on arms control, security trade and human rights at Amnesty, said in a statement. “Poor regulation and lack of oversight of the immense arms flows into Iraq going back decades have given (ISIS) and other armed groups a bonanza of unprecedented access to firepower.”

Amnesty’s report said “a large proportion” of the Islamic State’s weapons were originally given to the Iraqi military by the United States, Russia and the former Soviet Union. They range from handguns and assault rifles to anti-tank weapons and shoulder-mounted missile launchers, most of which were manufactured between the 1970s and 1990s. But the Islamic State has also been crafting its own weapons, such as hand grenades, car bombs and other explosive devices.

Amnesty said the diverse nature of the Islamic State’s weapons “reflects decades of irresponsible arms transfers to Iraq,” a country that saw its military stockpile swell when at least 34 countries began sending it weapons around the time of the Iran-Iraq war. Amnesty said the country began bringing in fewer weapons after it invaded Kuwait in 1990, largely due to a United Nations embargo, but its weapons imports spiked again after the United States invaded Iraq in 2003.

Amnesty reported that 30 countries have sent weapons to Iraq in the past 12 years, but many were not properly tracked by the Iraqi military or the U.S. military forces occupying the nation.

“Hundreds of thousands of those weapons went missing and are still unaccounted for,” the report states. It goes on to note that “mass desertion” from the Iraqi military during the rise of the Islamic State in 2013-14 “left huge quantities of military equipment exposed to looting.”

While the Amnesty report says the majority of the Islamic State’s weapons were looted from those military stockpiles, the document notes the group also added arms by seizing them from Syrian soldiers on battlefields and from defectors who have brought firepower with them.

Speaking to CNN, a Pentagon spokesman said the United States monitors the technology that it gives to its partners to prevent any American weapons from ending up in the wrong hands, but conceded those monitoring programs don’t include any weapons lost on battlefields.

Amnesty’s report calls for countries to stop providing military equipment and arms to forces in Syria and stronger protocols for sending weapons to Iraqi authorities. It also calls for national laws and procedures to prevent arms from ending up in the hands of groups who will use them nefariously, and for more strict rules regarding stockpile management and record-keeping.

“The legacy of arms proliferation and abuse in Iraq and the surrounding region has already destroyed the lives and livelihoods of millions of people and poses an ongoing threat,” Wicken said in a statement. “The consequences of reckless arms transfers to Iraq and Syria and their subsequent capture by (ISIS) must be a wake-up call to arms exporters around the world.”