MEXICAN President Claudia Sheinbaum said she would demand explanations over what United States and Mexican officials were doing in northern Chihuahua when they died in a car accident over the weekend.

The crash, following an operation to destroy a clandestine drug lab in a rural area, has reignited a debate over the extent of US involvement in Mexican security operations. 

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

Ms Sheinbaum said state governments must have authorisation from Mexico’s federal government to collaborate with US and other foreign entities “in line with the constitution.”

Chihuahua attorney general Cesar Jauregui said the officials died while returning from the operation to destroy labs of criminal groups in rugged mountain territory connecting Chihuahua to Sinaloa state, when the truck “appears to have skidded and fell into a ravine, exploding.”

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

The US embassy on Monday declined to identify who the US officials were or which entity of the US government they worked for, but said the officials were “supporting Chihuahua state authorities’ efforts to combat cartel operations.”