Federal authorities announced Wednesday the seizure of more than one million fentanyl pills during a four-state operation in October.

Between Colorado, Utah, Montana and Wyoming, officials seized over 1.05 million individual pills, over 3.5 kilograms of fentanyl powder — enough to yield more than 1.7 million additional pills — and over $500,000 in U.S. dollars, according to a Wednesday news release from the Rocky Mountain Field Division of the U.S. Drug Enforcement Agency.

“What we’re really trying to do is disrupt the supply chain that’s going by hitting so much fentanyl at one time,” said the RMFD’s Special Agent in Charge David Olesky in an interview with The Denver Gazette. “The cartels know that what we’ve been doing at the DEA and across the world, that we’re not going to tolerate fentanyl.”

Members of the Mexican Sinaloa and Jalisco cartels, both designated as foreign terrorist organizations, were involved in the supply chain network that brought the pills to the Rocky Mountain region, Olesky said.

The announcement continued what has been a recent string of drug busts by the agency. In mid-November, the RMFD, along with the Colorado Bureau of Investigation and the Douglas County Sheriff’s Office, announced the seizure of nearly two million fake fentanyl pills from an abandoned storage unit.

A week later, the agency announced it had seized more than 1,000 pounds of methamphetamine in a string of operations over an 11-month span, including a state record 733 pounds from one April bust. Members of the same cartels involved in the October fentanyl operation were also involved in the methamphetamine trafficking network.

The RMFD October operation was part of a nationwide effort to crack down on fentanyl trafficking and distribution networks, according to the release. As of Monday, DEA officials have seized more than 45 million fentanyl pills and over 9,000 pounds of fentanyl powder during similar operations.

Those operations, Olesky said, appear to be having a tangible effect on the supply chain networks, not only within the U.S. but also that of synthetic drug ingredients from overseas countries to production factories in Mexico.

“Based on our laboratory testing and our most recent numbers, right now three out of 10 pills contains a lethal dose of fentanyl,” Olesky said, adding that the rate was down from a high watermark of seven out of 10 pills at one point over the past half decade.

“The decrease in potency does show that somewhere in the supply chain they are being impacted, in the sense that they’re not as potent as they once were,” Olesky said. “Certainly the cartels know that the DEA is laser-focused not only on them, but the trafficking of fentanyl … it shows that we are not letting up and there’s a renewed sense of purpose in our work.”