Mexican drug cartels are beginning to smuggle marijuana from the U.S. into Mexico, once the undisputed grass basket for pot sold in the U.S., according to the Drug Enforcement Administration.

The alleged smuggling involves top-notch marijuana grown by American entrepreneurs in states that allow marijuana for recreational or medical use.

The anti-drug agency learned of high-quality marijuana being taken to Mexico from ongoing intelligence operations, says DEA spokesman Lawrence Payne.

"Traffickers who are operating in the U.S. are securing marijuana in the U.S. that is much higher quality and more expensive for the purpose of smuggling back into Mexico for sale and distribution," he tells U.S. News.

"Much of this marijuana is being grown [and] obtained in states that have relaxed their marijuana laws, such as Colorado," says Payne, who was unable to provide more specific information on the alleged smuggling and unable to identify recent prosecutions for southbound smuggling.

"Unfortunately, I don't have any specific information or numbers to quantify other than to say we know that it's happening," he says. "[It's] too early to really know the level or scale of the trafficking southward."

NPR first reported Monday the DEA's allegation that U.S.-grown marijuana is being smuggled to Mexico, particularly from Colorado by the Sinaloa cartel. Payne told the broadcaster: "It makes sense. .... If you can buy some really high-quality weed here, why not smuggle it south, too, and sell it at a premium?"

The thrust of NPR's report was that legalization in the U.S. is driving down prices for marijuana grown in Mexico. Eliminating violence associated with the black market and undercutting organized crime are key arguments for marijuana legalization supporters.

Colorado and Washington currently are the only states with recreational marijuana stores. The states, where shops opened in January and July, respectively, allow adults 21 and older to possess up to 1 ounce of marijuana.

Many other states, including California, allow marijuana for treatment of various medical conditions. Residents of Alaska, Oregon and the District of Columbia voted in November to legalize recreational marijuana use, but stores are not yet open there.

Mason Tvert, communications director for the Marijuana Policy Project and a co-director of the successful 2012 campaign to legalize pot in Colorado, is skeptical of the DEA's claims.

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"It's certainly interesting if it is actually the case, but we should probably wait until there is confirmation that it's even happening before we jump to conclusions," he says. "Unfortunately, the DEA doesn't have a great track record when it comes to providing objective information about marijuana."

The agency's administrator, Michele Leonhart, is an outspoken opponent of marijuana legalization. During a 2012 congressional hearing she refused to say marijuana is less harmful than crack cocaine or heroin, and in January she condemned President Barack Obama's observation that marijuana use is less harmful than drinking alcohol, prompting a campaign by pot advocates urging her dismissal.