MEXICO CITY (AP) — Mexican President Claudia Sheinbaum said Monday she would demand explanations over what U.S. and Mexican officials were doing in northern Chihuahua when they died in an accident over the weekend, noting that any joint collaborations between the local government and the U.S. without federal permission would be a violation of Mexican law.

The crash, following an operation to destroy a clandestine drug lab in a rural area, has reignited a debate over the extent of U.S. involvement in Mexican security operations. Speculation was only fueled by Sheinbaum, local officials and the U.S. Embassy appearing to contradict each other and at times themselves, and offering sparse details about the U.S. officials who died.

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

It comes at a key moment for the relationship between the two neighboring nations as Mexico faces escalating pressure from U.S. President Donald Trump crack down on cartels and Sheinbaum underscores Mexico’s sovereignty.

Sheinbaum said her government would investigate the incident to ensure no laws were broken after the deaths on Sunday, adding that state governments must have authorization from Mexico’s federal government to collaborate with U.S. and other foreign entities “as established by the Constitution.”

A mountainside car crash

Chihuahua Attorney General César Jáuregui said Sunday the officials died while returning from the operation to destroy labs of criminal groups. They were driving in the middle of the night through rugged mountain territory connecting Chihuahua to the state of Sinaloa, when the truck “appears to have skidded at some point and fell into a ravine, exploding.”

He said the four who died were two local Mexican investigative officials and two U.S. Embassy instructors who were participating in routine “training work.”

The U.S. Embassy on Monday declined to identify who the U.S. officials were or which entity of the U.S. government they worked for, but said the officials were “supporting Chihuahua state authorities’ efforts to combat cartel operations.” U.S. Ambassador Ronald Johnson expressed his condolences on social media but he and other officials provided few details of the incident.

Jáuregui said that the operation came following months of investigation by state prosecutors and Mexico’s federal military, indicating there was at least some level of involvement in the operation from Sheinbaum’s security forces. Hours later, the Mexican Security Cabinet confirmed that the army and state prosecutor’s office carried out a joint operation over the weekend in Chihuahua dismantling drug labs in the same location, Morelos.

After locating the labs using drones, officials found tons of material to manufacture drugs but no people, who were likely alerted beforehand and fled, the prosecutor added.

The local official later backtracked and clarified to press that there “were no U.S. agents in the operation to secure the narco-lab,” and said the embassy officials joined the group after the operation and were several hours away from where the action took place.

A resurfaced debate

Sheinbaum said her government would provide more information when it has more details, but insisted Monday that “there are no joint operations on land or in the air” in Mexico. She said there is only sharing of information between her government and the U.S., carried out within a “well-established” legal framework.

While U.S. officials’ training of Mexican security forces is common, their presence on Mexican territory has been the subject of ongoing debate, which has intensified after Trump’s military actions in Venezuela and Iran.

Trump has repeatedly offered to take action on Mexican cartels, intervention which Sheinbaum has said was “unnecessary. ” The Trump administration has already launched joint military operations in Ecuador, a country that has been roiled by violence by drug gangs in recent years.

Last year, Sheinbaum said the U.S. had conducted surveillance drone flights at Mexico’s request after a series of conflicting public statements on the issue, also sparking alarm among observers.

The most recent controversy surfaced in January over the detention in Mexico of former Canadian athlete Ryan Wedding, one of the United States’ most wanted fugitives. While Mexican officials claim he surrendered at the U.S. Embassy, U.S. authorities have described his capture as the result of a binational operation.

The recent debacle comes at a pivotal time in U.S.-Mexico relations. The second round of negotiations between the United States and Mexico on the United States-Mexico-Canada free trade agreement, the USMCA, was slated to begin in Mexico City. The U.S. delegation is led by Trade Representative Jamieson Greer, who was scheduled to meet with the president on Monday.

That same day, the Trump administration also announced it was imposing visa restrictions on family members of the Cartel de Sinaloa.

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