Denver police officers, some in hazmat suits, raided multiple marijuana-growing operations Tuesday, part of an investigation into illegal marijuana sales in Minnesota, a federal law enforcement official said.

Federal agents assisted in the raids, which saw investigators haul dozens of high-intensity grow lights and thousands of plants out of the operations. The federal official said as much as $1 million was found in large bags during the searches.

The official, who was not authorized to disclose information about the case and spoke to The Associated Press on the condition of anonymity, said investigators believe the people involved came to Colorado from Minnesota, where marijuana is illegal outside of a restrictive medical-marijuana program.

Officially, authorities released little information about the case.

On Twitter, Denver police wrote that the investigation involved “illegal drug activity.” But a spokesman for the department later said he did not know if the operations raided were licensed marijuana businesses or if detectives believe they were exclusively illegal.

Denver police did not announce any arrests connected to the raids.

A spokeswoman for the state Marijuana Enforcement Division, which regulates cannabis businesses, refused to comment on whether the division was involved in the investigation. Likewise, James Gothe, group supervisor of the Drug Enforcement Administration’s special support unit in Denver, offered little comment.

“It’s a very large and successful investigation,” Gothe said.

At one raided site — on North Bryant Street, near West Sixth Avenue — a Denver police officer was seen entering a building in a blue hazmat suit. The officer, his suit reeking of marijuana, said several search warrants were being executed around the city.

The raided building on North Bryant Street is in an industrial area popular with state-legal commercial marijuana growers and, increasingly, illegal growers trying to hide among them. The raided address was once home to the grow operation for a medical-marijuana products business, state records show, but it is unclear whether the business is still there.

Cannabis industry insiders said they believe the address is now occupied by people claiming to be medical-marijuana caregivers — smaller-scale providers that operate with less scrutiny.

At neighboring cannabis businesses, employees were bewildered by the flurry of police activity.

Naté Perini, who works at edibles manufacturer Edi-Pure, which is next door to the raided operation on North Bryant Street, said the cops already were there when she got to work around 9 a.m.

“Yeah, they’re getting raided,” she said.

A police car was parked in front of the shop and another was parked in the alley behind it. Police tape had been strung around the perimeter.

Tuesday’s raids came 11 months after local and federal authorities raided several large marijuana businesses — the largest raids on Colorado pot businesses since medical marijuana became legal. Four people connected to the businesses raided then have been charged with federal crimes, and prosecutors also have moved to seize the businesses’ assets.

Staff writers Ricardo Baca and Kirk Mitchell and the Associated Press contributed to this report.