US Customs and Border Protection officers in Arizona said they recently made the single-largest bust of fentanyl in the agency’s history after seizing 4 million pills from a 20-year-old man.

The historic bust occurred early last month after the man arrived at the Lukeville port of entry driving a pickup truck that was hauling a sport recreational vehicle on a utility trailer, the CBP said in a news release on Thursday.

The man, who authorities said is from Arizona, and his vehicles were sent for a more intensive inspection following officers’ initial US entry inspection, according to the release.

During the second inspection, officers discovered “anomalies” with the trailer’s frame, according to the release. Officers and a canine team then found 234 packages of drugs hidden in the frame.

The packages contained around 4 million blue fentanyl pills weighing more than 1,000 pounds, according to the agency.

“This is the largest fentanyl seizure in CBP’s history, and reflects our unwavering determination to protect our nation and to disrupt the criminal activities of ruthless drug cartels,” said CBP Senior Official Performing the Duties of the Commissioner Troy Miller.

The seizure was part of the CBP’s Operation Apollo-Arizona and Operation Plaza Spike, which focus on collecting fentanyl-related intelligence and disrupting cartel operations that facilitate the flow of fentanyl, respectively. The CPB has seized more than 15,000 pounds of fentanyl so far in 2024, federal data show.

Fentanyl, a strong synthetic opioid that is about 50 times more potent than heroin, was involved in almost 70% of overdose deaths last year, according to data from the US Centers for Disease Control and Prevention’s National Center for Health Statistics. The narcotic kills tens of thousands of people in the US annually.

President Joe Biden on Wednesday called on federal agencies and Congress to take actions to curb the flow of fentanyl into the US, CNN previously reported.

Biden said a national security memorandum “will increase intelligence collection on traffickers’ evolving tactics to smuggle narcotics into our country” and help law enforcement agencies seize more of the drugs before they reach communities.

The US Drug Enforcement Administration says it has seized more than 30 million fentanyl pills and more than 4,100 pounds of fentanyl powder this year, representing more than 208 million deadly doses.

CNN’s Samantha Waldenberg and Deidre McPhillips contributed to this report.