Mexican President Claudia Sheinbaum announced Monday that her government delivered a diplomatic note to the United States regarding the unauthorized presence of US officials during an anti-narcotics operation in the northern state of Chihuahua.

The incident came to light after a car crash on April 19 that killed four people: two US officials and two Mexican officials. The crash occurred following the completion of the anti-drug operation. Multiple reports have identified the US officials as CIA officers, though this has not been officially confirmed by either government.

Sheinbaum stated that the federal government was not aware of the US officials' participation in the operation until after the fatal accident occurred. The president emphasized that such unauthorized involvement should not happen again, according to the contents of the diplomatic note sent to Washington.

The incident highlights ongoing tensions over US involvement in Mexico's anti-narcotics efforts and questions about coordination between the two countries' law enforcement and intelligence agencies. The specific details of the operation that preceded the crash have not been disclosed by either government.

Separately, the US Embassy in Mexico issued a security alert Monday ordering government employees to avoid the border city of Reynosa due to reports of violent criminal activity, including roadblocks. The embassy's consulate in nearby Matamoros reported receiving multiple accounts of such incidents in the area near the Texas border.