Court documents in the US allege Mexico's former defence secretary helped a cartel smuggle thousands of kilograms of cocaine, heroin, methamphetamine and marijuana into the United States in exchange for bribes.
General Salvador Cienfuegos, 72, is accused of acting on behalf of the H-2 cartel while defence secretary from 2012 to 2018 under former President Enrique Pena Nieto.
Thousands of intercepted messages show the general ensured military operations were not conducted against the cartel, and that operations were initiated against rivals, according to prosecutors.
Cienfuegos - also known as "El Padrino," or "The Godfather," according to the indictment - is accused of alerting cartel leaders to a US investigation into its operations and the use of cooperating witnesses and informants, which resulted in the murder of a cartel member wrongly believed to be assisting US authorities.
US authorities said in court documents that the cartel had numerous distribution cells in the US when Cienfuegos led the Mexican military, including Los Angeles, Las Vegas, Ohio, Minnesota, North Carolina and New York.
In Mexico, the cartel is accused of trafficking hundreds of firearms and committing "countless acts of horrific violence, including torture and murder, in order to protect against challenges from rival drug trafficking organisations, fight for territory and silence those who would cooperate with law enforcement."
Cienfuegos made an initial court appearance by video from his Los Angeles detention facility on Friday, wearing a dark-coloured jacket and a face mask.
US District Judge Alexander MacKinnon ordered Cienfuegos held without bail until a hearing on Tuesday in Los Angeles, after prosecutors arged he was a major flight risk.
Cienfuegos is the highest-ranking former Cabinet official arrested since top Mexican security official Genaro Garcia Luna was taken into custody in Texas in 2019. Garcia Luna, who served under former President Felipe Calderon, has pleaded not guilty to drug trafficking charges.
Mexico's current president, Andres Manuel Lopez Obrador, has vowed to go after corruption and lawbreaking under past administrations, but he has relied more heavily on the army - and given it more responsibilities - than any other president in recent history.
Lopez Obrador sought on Friday to reassure the country that he still had faith in the armed forces as "pillars of the Mexican state."