Mexican President Claudia Sheinbaum told reporters on Wednesday that the Mexican military was unaware of the presence of U.S. agents who died in a car accident during an antidrug operation in the border state of Chihuahua.

"Evidently, the military didn't know there were people participating who weren't Mexican citizens ... that there were foreigners participating in the operation," Sheinbaum told reporters. "This is something that Mexicans shouldn't take lightly."

The two Americans killed in the crash were employees of the Central Intelligence Agency, multiple people familiar with the matter told CBS News. The CIA declined to comment. 

Sheinbaum said the federal government is still investigating a potential violation of national security laws in the still-murky incident.

Mexican authorities said the Americans died alongside two Mexican officers and had taken part in a raid on a clandestine drug lab in the northern state's remote sierra.

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

The five-car convoy included soldiers and members of the Chihuahua State Investigation Agency, authorities said.

The U.S. agents killed were "instructor officers" who "were carrying out training tasks" as part of binational anti-drug cooperation, state prosecutor Cesar Jauregui told reporters. Jauregui called the targeted labs "one of the largest sites found in the country where chemical drugs were produced."

U.S. Ambassador Ronald Johnson expressed his condolences on social media but he and other officials provided few details of the incident.

"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.

On-the-ground cooperation between U.S. law enforcement and Mexican security forces is historically rare and a politically sensitive topic in the country. Sheinbaum has publicly rejected the practice.

Home to the key border city of Juarez, Chihuahua is one of only four out of 31 states governed by the conservative National Political Action party (PAN), which opposes Sheinbaum's left-leaning Morena party.

The leader said she planned to meet with the Chihuahua state governor to discuss the incident.

Sheinbaum has resisted the Trump administration's threats to use airstrikes or ground troops to fight Mexican cartels, instead promoting intelligence sharing with the U.S. while local security forces attack crime groups.

Elite Mexican troops operating with U.S. intelligence killed drug kingpin Nemesio "El Mencho" Oseguera in February, unleashing a wave of violence that left over 70 dead.

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

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.