PHOENIX — US Customs and Border Protection officials announced Thursday their biggest fentanyl bust ever, saying they captured nearly 254 pounds (114 kilograms) of the synthetic drug that is helping fuel a national epidemic of fatal opioid overdoses from a secret compartment inside a load of Mexican produce heading into Arizona.

The drug was found hidden Saturday morning in a compartment under the rear floor of a tractor-trailer after a scan during a secondary inspection indicated “some anomalies” in the load, and the agency’s police dog team alerted officers to the presence of drugs, Nogales CBP Port Director Michael Humphries said.

Most of the seized fentanyl with an overall street value of about $3.5 million was in white powder form, but about 2 pounds of it (1 kilogram) was contained in pills. Agents also seized nearly 395 pounds (179 kilograms) of methamphetamine with a street value of $1.18 million, Humphries said.

The Drug Enforcement Administration said the previous largest US seizure of fentanyl had been in August 2017 when it captured 145 pounds (66 kilograms) of the drug in a Queens, New York, apartment that was linked to the Sinaloa cartel. Before that, the largest recorded fentanyl seizure was 88 pounds (40 kilograms) nabbed from a pickup truck in Bartow County, Georgia.