The so-called Islamic State (or Daesh) maintained a significant arsenal of weapons originally purchased by the United States.

A new report from Conflict Armament Research (CAR) reveals that a startling number of weapons bought by the U.S. ended up in the hands of Daesh. Allegedly, these weapons were originally handed-off to rebel groups in Syria supported by the U.S. and its international coalition of allies.

However, they quickly ended up in Daesh hands, sometimes within a matter of just a couple of months from the date of purchase, according to BuzzFeed. The report suggests this occurred due to constantly shifting alliances in the Syrian conflict, which often saw rebel groups backed by the U.S. working directly or indirectly with groups such as Daesh.

While most of the terrorist group's weapons analyzed by the report appear to have been looted from the Syrian and Iraqi militaries, many were supplied by the U.S. and other anti-Assad allies.

The number of U.S. purchased weapons controlled by Daesh goes "far beyond those that would have been available through battle capture alone," the report points out.

"Iraq and Syria have seen IS forces use large numbers of weapons, supplied by states such as Saudi Arabia and the United States, against the various international anti-IS coalitions that the two states support," the report continues.

The report traced the origins of more than 40,000 weapons. Altogether, Western weapons – whether captured or introduced directly to the conflict – made up 10 percent of the total counted by the monitoring group.

"Evidence collected by CAR indicates that the United States has repeatedly diverted EU-manufactured weapons and ammunition to opposition forces in the Syrian conflict,” the report explains. Daesh "rapidly gained custody of significant quantities of this materiel."

When confronted by The Washington Post, Defense Department spokesman Eric Pahon did not dispute the report's findings. 

"Wherever possible, our advisers will monitor the use of the weapons and supplies we give the [Syrian Democratic Forces], ensuring use only against ISIS [Daesh]," Pahon said. 

"Any alleged misuse or diversion of U.S. support will be taken seriously and lead to the possible curtailment of support, if verified," he added.

The controversial U.S. decision to provide aid and weapons to rebels fighting President Bashar al-Assad's government forces in Syria has been plagued by criticism and allegations that weapons ended up in Daesh hands for several years. The clandestine program, launched by President Barack Obama, was quietly ended by the new administration of President Donald Trump at the beginning of the summer.

"This is a big deal, but it’s been a long time coming,” Charles Lister, a Syria analyst for the Middle East Institute in Washington told The New York Times in July, discussing Trump's decision to stop sending weapons and aid to Syrian rebels. 

“It’s the biggest indication so far of the administration’s having given up on the opposition," he added.

However, considering the new report's findings, it's only logical that the U.S. would stop sending weapons that have consistently ended up in the hands of its declared enemies.