DENVER — Federal authorities descended unexpectedly Thursday morning on multiple Colorado medical-marijuana operations, seizing plants and executing search warrants at shops suspected of running afoul of Justice Department guidelines on pot.

Jeff Dorschner, spokesman for the U.S. attorney in Colorado, said in a statement that the raids in Denver and Boulder were part of an ongoing investigation.

“While the investigation is ongoing, there are strong indications that more than one of the eight federal prosecution priorities identified in the Department of Justice’s August guidance memo are potentially implicated,” said Mr. Dorschner.

Those priorities — federal rules regarding marijuana that the Justice Department has said must be followed even in jurisdictions where marijuana laws have been loosened — include preventing the sale and distribution to minors; preventing revenue from sales from going to criminal enterprises, and preventing the diversion of marijuana to neighboring states where the drug is banned.

The Colorado raid is the latest example of tensions over marijuana triggered by the disconnect between federal and state pot laws. The Justice Department has given states leeway to proceed with controlled medical-marijuana operations even though the sale and possession of marijuana is prohibited under federal law.

That disconnect is likely to intensify Jan. 1, when Colorado and Washington launch the nation’s first regulatory markets for recreational marijuana. Voters in both states agreed in the November 2012 election to decriminalize recreational pot use for adults 21 and older.

Agents with the Drug Enforcement Administration conducted raids on Washington state medical-marijuana dispensaries in July, while California and Montana operations have also been the targets of federal crackdowns in recent years.

Mason Tvert, spokesman for the Marijuana Policy Project, said he was still waiting for details Thursday about what provoked the Colorado raid.

“The Justice Department said it would respect states’ rights to regulate marijuana, and that it would not go after businesses as long as they are complying with state laws,” Mr. Tvert said in a statement. “We hope they are sticking to their word and not interfering with any state-regulated, law-abiding businesses.”

Agents from the Drug Enforcement Administration, Internal Revenue Criminal Investigations, Denver Police Department and state and local law enforcement began Thursday morning “executing lawfully obtained search warrants and seizure warrants,” said Mr. Dorschner.

Agents carried out the raids in Denver and Boulder in spite of snow and below-freezing temperatures. The Boulder Daily Camera posted a photo online of a large pile of green plants sprinkled with snow outside a north Boulder grow operation.

“One important note: Although we cannot at this time discuss the substance of this pending investigation, the operation underway today comports with the department’s recent guidance regarding marijuana enforcement matters,” Mr. Dorschner said.

Deputy Attorney General James M. Cole issued an Aug. 29 memo after the Colorado and Washington votes spelling out the Justice Department’s eight enforcement priorities on marijuana, warning that federal officials may intervene if state and local authorities fall short.

“If state enforcement efforts are not sufficiently robust to protect against the harms set forth above, the federal government may seek to challenge the regulatory structure itself in addition to continuing to bring individual enforcement actions, including criminal prosecutions, focused on those harms,” Mr. Cole said in the memo.

In November, Colorado voters approved Proposition AA, a state excise and sales tax on retail marijuana. Its supporters argued that the additional taxes were needed to fund a vigorous regulatory and enforcement network for recreational pot.

Mr. Tvert, who led the campaign to decriminalize recreational pot, said he wants marijuana businesses to be treated fairly by law enforcement, but he also doesn’t expect special treatment.

“Colorado has demonstrated that regulating marijuana works,” he said. “Those businesses that are in clear compliance with state laws are meeting the needs of the community and not causing problems.”

Those businesses that do violate state laws “will likely face consequences. That is how our society treats alcohol, and that is how we expect to see marijuana treated,” Mr. Tvert said.

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