SAN DIEGO -- The son of a leader of Mexico's Sinaloa cartel has been indicted on drug smuggling charges in the United States and pleaded not guilty on Monday, less than two weeks after surrendering to U.S. border inspectors.

Damaso Lopez Serrano was held without bail after a brief appearance in federal court in San Diego. He is the son of Damaso Lopez Nunez, who has launched a struggle for control of the cartel following the arrest of its leader, Joaquin "El Chapo" Guzman.

Guzman was extradited to the United States earlier this year to face drug charges.

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The elder Lopez was arrested by authorities in Mexico City in May. Known by the nickname "El Licenciado," a title for college graduates, he was long considered Guzman's right-hand man and helped him escape from Mexican prison in 2001.

The elder Lopez is believed to have been locked in a dispute with Guzman's sons for control of the cartel's territories. The head of Mexico's federal detectives' agency, Omar Garcia Harfuch, said in May that Lopez was "one of the main instigators of violence" in the Mexican states of Sinaloa and the southern part of Baja California.

Lopez's son, known as "Mini Lic," turned himself in to U.S. Customs and Border Protection officers on July 27 in Calexico, California, across the border from Mexicali, Mexico, said Adam Braverman, an assistant U.S. attorney.

The indictment, which was filed in August 2016 and ordered unsealed Monday, charges Lopez Serrano with conspiracy to import and distribute methamphetamine, cocaine and heroin.

Braverman told U.S. District Judge Dana Sabraw that the investigation lasted five years and involved intercepts of more than 250 communication devices. In 2015, there were tens of thousands of communication intercepts and "a number of (drug) seizures" in Mexico and the United States.

Lopez Serrano appeared in an orange uniform for jail inmates and said little in court.

His attorney, Michael Littman, entered the not-guilty plea on his client's behalf. Littman declined to comment as he left the courtroom.