Four people, including two American embassy workers, were killed in a car accident following a major drug raid in northern Mexico, prosecutors said Sunday.

On Friday and Saturday, six clandestine synthetic drug labs were raided in Morelos, in the northern state of Chihuahua, after a three-month investigation, state prosecutor César Jáuregui told reporters.

Jáuregui initially said the accident happened while the officers were returning from the drug raids, but after Mexican President Claudia Sheinbaum said she was unaware of any U.S. participation in the operations, the prosecutor later said the Americans weren’t involved in those operations. 

“It was not an operation that the security cabinet was aware of,” Sheinbaum told journalists on Monday, according to The Associated Press. “We were not informed; it was a decision by the Chihuahua government.” 

Sheinbaum said she would demand an explanation and noted any such collaboration would need to be approved by the federal government, “as established by the Constitution,” the AP reported.

Jáuregui then clarified later Monday, “That operation involved the participation solely of agents from the State Investigation Agency and the Mexican navy.”

Jáuregui said the Americans were “primarily engaged in training activities, located some eight to nine hours away from the site where the operation was taking place.” He said they met with the director of the State Investigation Agency later, when he was on his way back from the raid.

“They were not coming from the operation. That is why, obviously, the president stated that we were not apprised of their participation,” Jáuregui said. “It was simply taken for granted that they had participated in the operation itself. I was notified of this at 2:00 in the morning. The information I had to provide was simply the information I possessed at the time.”

The victims’ vehicle, which was leading an official convoy of five cars, skidded off the road and plunged into a ravine, Jáuregui said over the weekend.

The Americans killed were “instructor officers” who specialize in training on drones and other tactics, Jáuregui said.

Jáuregui called the labs “one of the largest sites found in the country where chemical drugs were produced.”

In a news release, the state attorney general’s office identified two of the crash victims as first commander of the state investigation agency Pedro Román Oseguera Cervantes and officer Manuel Genaro Méndez Montes.

“We extend our deepest condolences and our sympathies to the families of those who died in this tragic accident,” the office said in a statement.

The identities of the two U.S. Embassy officials killed in the crash were not released. U.S. Ambassador Ronald Johnson paid tribute to the victims in an X post.

“We honor their dedication and tireless efforts to confront one of the greatest challenges of our time,” Johnson said.

“This tragedy is a solemn reminder of the risks faced by those Mexican and U.S. officials who are dedicated to protecting our communities,” he said, adding it “strengthens our resolve to continue their mission.”

Mexico has announced the dismantling of numerous drug labs in recent months after President Trump threatened possible military action to curb cartels in the country. 

In February, Mexican naval personnel discovered a hidden drug laboratory in the country’s Durango region and “neutralized” over 5,000 pounds of methamphetamine. In January,  authorities announced more than 1,500 pounds of meth were seized from clandestine laboratories in the states of Durango, Sinaloa and Michoacán.