(CNN) Federal authorities suspect that thousands of machine gun conversion devices have been illegally imported into the United States from China, in some cases ending up in the hands of convicted felons, CNN has learned.

Agents with the federal Bureau of Alcohol, Tobacco, Firearms and Explosives are actively working to locate the devices and retrieve them.

Brad Engelbert, an ATF spokesman, described the nationwide recovery effort as a "high priority" for the agency, focused on those devices in the possession of "people who may be a danger to the community."

"We're working it," Engelbert said. "We want to nip this in the bud. We want to get these things off the street."

He declined to provide details about the number of devices recovered, but said some had been taken from convicted felons.

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Unlicensed dealers provide a flow of weapons to those who shouldn't have them, CNN investigation finds ATF and customs officials in Chicago identified more than 2,900 packages containing conversion devices "that are believed to have been shipped into the United States" under false customs declarations, according to an affidavit filed in federal court in Rhode Island. The devices render semi-automatic Glock pistols into fully automatic weapons and are considered a machine gun in and of themselves under federal law. While the devices are specifically designed to modify Glock pistols, Engelbert, the ATF spokesman, stressed that they are not manufactured by Glock. PayPal accounts linked to the suspected Chinese exporter -- "revealed over 3,800 sales transactions by US customers who are believed to have illegally purchased and obtained" the weapons, according to court records. Agents with the ATF's Internet Investigations Center recently purchased "multiple" conversion devices from a website "believed to be operated out of China" by one or more suspects, according to the affidavit. The conversion devices were sold for $19.99 each and advertised as "Glock Pistols Select of switch Full Auto For All models Glock all Generations." Shipping labels, however, described them as "MULTITOOL SWITCH" and/or "HANDCRAFTED FINISHED PIECES." One gun's path to destruction

It is illegal for civilians in the United States to possess machine guns manufactured after 1986. Ownership of a machine gun made before then requires a federal permit and registration. The relatively small amount of fully automatic weapons available for purchase has created a niche market in which they can sell for tens of thousands of dollars.

Jill Snyder, a recently retired supervisory agent with ATF, said the fact that there's no lawful use for the devices raises troubling questions about who is attempting to acquire them.

"They're not for hunting," she told CNN. "They're not for home protection." Rather, Snyder said, she worried they may appeal to criminals interested in "drive-bys and mass shootings."

Attempting to locate and recover them, she said, presents an obvious danger: "You've got agents knocking on the doors of people potentially armed with fully automatic weapons."

Among the Chinese website's suspected customers is a convicted felon from Rhode Island named David Poole, according to court records. Poole is suspected of purchasing at least two of the devices and was charged earlier this month in federal court in Providence with being a felon in possession of a weapon and possession of a machine gun.

Poole is described in court records as "a known drug user" with eight previous arrests and a 2014 felony conviction for receiving stolen property.

According to court records, he recently provided his girlfriend cash to buy him four guns, including three Glock pistols, totaling more than $2,500 in value. Poole was arrested shortly after the devices for converting Glocks to automatic weapons were delivered to his home, the records state.

Poole allegedly told agents he acquired the devices "for home protection."

Contacted by CNN, Poole's attorney declined comment. The case is pending.

In April, agents raided a home in Missouri linked to man suspected of buying 13 conversion kits from the website of a Chinese company. The company is not identified in the court filing, but language used to advertise the devices matches that on the site referred to in the Rhode Island court affidavit.

Records obtained via a search warrant revealed that Garnell Carter used his PayPal account to purchase the devices, according to an affidavit filed in St. Louis federal court.

Agents seized six of the devices and found packaging "consistent with Carter having received more" of the devices.

One occupant of the house told agents Carter said he knew how to convert Glock pistols to automatic weapons and offered to do so for the person, the affidavit states.

Carter has pleaded not guilty. His attorney also declined comment when contacted by CNN.

The conversion devices have also been recovered in Illinois and California, according to court filings and news accounts.

Snyder, who most recently ran the San Francisco Division of the ATF before retiring from the agency last fall, said she previously worked on cases involving similar devices being illegally exported from the Philippines.

She said the devices don't have serial numbers on them and are impossible to track if not recovered in the possession of the original purchaser. She added that, just because ATF was aware of one company's sales, that doesn't mean that there aren't others going undetected.

"That sounds like a significant number," she said of the ongoing investigation into the Chinese website. "How many other thousands are there that we don't know about?"