Mexican officials confirmed on Thursday that they had issued an arrest warrant for the prominent boxer Julio César Chávez Jr. on charges of involvement in organized crime and arms trafficking, a day after he was detained by U.S. immigration authorities in California.

Mr. Chávez had been detained by federal U.S. agents in Studio City, Calif., the Department of Homeland Security said on Thursday, citing the arrest warrant in Mexico and saying that Mr. Chávez was in the United States illegally.

A spokesman for Mexico’s Attorney General’s Office said that the U.S. authorities had informed Mexican officials about the detention, and said “they have started the corresponding procedure for his extradition to Mexico.” The warrant for him was issued in March 2023, the spokesman said.

Lawyers for Mr. Chávez could not immediately be reached for comment.

A former World Boxing Council middleweight champion, Mr. Chávez, 39, was detained just days after he lost a high-profile boxing match in Anaheim, Calif., against the former YouTuber Jake Paul. He is also the son of a Mexican boxing legend, Julio César Chávez Sr., who appeared with Mexico’s president twice in recent months, at a news conference and a government event in Mexico City that drew tens of thousands of people.

The Department of Homeland Security said in its statement that Mr. Chávez was “also believed to be an affiliate of the Sinaloa Cartel,” referring to the powerful crime syndicate that the U.S. and Mexican authorities have targeted in an aggressive crackdown.

The U.S. authorities said that Mr. Chávez had entered the United States legally in 2023 with a B2 tourist visa, but that it had expired in 2024. He then filed for lawful permanent resident status based on his marriage to a U.S. citizen, who U.S. officials said was “connected to the Sinaloa Cartel through a prior relationship” with a son of the cartel leader Joaquín Guzmán Loera, known as El Chapo.