MEXICO CITY — Mexican officials said Sunday that they had captured a leader of the Juárez Cartel, Jesús Salas Aguayo, the man in charge of the gang’s operations in Ciudad Juárez during a convulsion of violence that made the city one of the world’s most murderous.

Mr. Salas, 38, was arrested Friday in the town of Villa Ahumada, about 80 miles south of the Texas border, Mexico’s national security commissioner told reporters Sunday. Mr. Salas took over the cartel’s leadership this year after the arrests of its boss, Vicente Carrillo Fuentes, last October and his replacement, David Aaron Espinoza Haro, in January, the commissioner said.

The arrest occurred the same day that security forces captured the leader of the Gulf Cartel, José Tiburcio Hernández Fuentes, in the city of Reynosa. That arrest set off hours of street fighting Friday, as about 60 of Mr. Hernández’s gunmen seized buses and set fire to them to block roads and shot at government buildings in a failed effort to prevent his transfer to Mexico City, said the security commissioner, Monte Alejandro Rubido, on Saturday.