Mexico's government said Saturday that two U.S. federal agents recently killed in a car crash in the country's northern region were not authorized to participate in operations in Mexico.

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

The role of the two CIA agents, who were returning from destroying a clandestine drug lab in the northern Mexican state of Chihuahua, remains unclear.

Local government officials have said they were part of a convoy when their car drove off a ravine last weekend and the vehicle exploded. Two Mexican officers were also killed.

A statement from Mexico's Ministry of Security said one U.S. agent entered Mexico as a visitor while the other entered with a diplomatic passport.

"None had formal accreditation to participate in operational activities in national territory," the security ministry said. 

It also asserted that Mexico's government was not aware of foreign agents operating or planning to participate in an operation on its soil. The ministry said it is reviewing the case with local authorities and the U.S. Embassy in Mexico.

"Mexican law is clear: it does not permit the participation of foreign agents in operations within the national territory," the ministry said in a statement.

It added: "The Government of Mexico reiterates its willingness to maintain a close, serious, and respectful relationship with the Government of the United States for the benefit of the security of both countries."

Officials from both countries have offered contradictory accounts on the issue, with Mexican President Claudia Sheinbaum admitting on Wednesday that federal forces were involved after Mexico's government said it had no knowledge of any operation or U.S. involvement.