MEXICO CITY (AP) —

Mexican prosecutors announced Friday they have seized a half-million fentanyl pills in a raid at a warehouse in the northern city of Culiacan.

The statement came one day after the army announced a “historic” seizure of over a half-ton of fentanyl at another warehouse in Culiacan, the capital of Sinaloa state, home to the cartel of the same name.

The enormous seizures came just days before President Andrés Manuel López Obrador is scheduled to visit Washington to meet with President Joe Biden.

In the raid announced Friday, and carried out Thursday, soldiers also found 83 kilograms of powder fentanyl and about a ton of meth, in addition to bales of pills.

Mexican cartels manufacture the synthetic opioid from precursors imported from China, and then press the drug into counterfeit pills made to look like Xanax, Adderall or Oxycodone.

On Thursday, Mexico’s army and National Guard announced what they called a “historic” seizure of over a half-ton of fentanyl at another Culiacan warehouse.

“This is the largest seizure in the history of this lethal drug,” said Assistant Public Safety Secretary Ricardo Mejia, estimating the fentanyl had an illicit value of around $230 million.

Synthetic opioids like fentanyl have been behind a major increase in overdose deaths in the United States; as little as two milligrams of fentanyl can be lethal. The drug is 100 times more potent than morphine.

The nearly 1,200 pounds (543 kilograms) found at the warehouse could have produced millions of the counterfeit pills in which fentanyl is usually offered. Fentanyl is so deadly because it is pressed into pills made to look like Xanax, Adderall or Oxycodone, or mixed into other drugs.

That has lead to tens of thousands of overdose deaths in the United States because people often do not realize they are taking fentanyl.

However, the purity of the amount found at the warehouse was unclear; fentanyl is often cut with other substances before being pressed into pills. Almost all of the fentanyl smuggled into the United States comes from Mexico, where it is produced with precursor chemicals smuggled from China.