Mexican President Claudia Sheinbaum is demanding answers from U.S. officials after two American personnel were killed alongside two Mexican investigators in a car crash following a counternarcotics operation in northern Mexico.

The four officials died Sunday in the state of Chihuahua when their vehicle veered off a mountainous road, plunged into a ravine, and exploded as they returned from activities linked to the dismantling of a clandestine drug laboratory, according to Mexican authorities.