massacre of 10 young people and children traveling in a pickup truck in Durango State.

Mexico reeled Monday from another bloody weekend of drug-related killings that was made even more horrible by the baffling massacre of 10 young people and children traveling in a pickup truck in Durango State. With 21 people killed across the nation on Sunday, the only break in the bleak news was the announcement that a reputed street-gang leader had been arrested in connection with the slayings of three people with ties to the United States Consulate in Ciudad Juárez on March 13. The young people slain in Durango were traveling from a farming community where they lived to the town of Los Naranjos to collect federal financial aid for students, prosecutors said in a statement. A man in military garb waved the pickup to a stop, the authorities said. Then he and an unknown number of other attackers riddled the truck with bullets and threw grenades at the occupants. The victims ranged in age from 8 to 21 — five girls and five boys from three families. Though the motive remained unknown, Federal Interior Secretary Fernando Gómez-Mont noted Monday that the Sinaloa drug gang had been waging a war in the region with the Zetas, former commandos and assassins who have splintered off from the Gulf cartel to form their own drug trafficking organization. Meanwhile, the authorities in Chihuahua State said they had arrested a reputed leader of the Barrio Azteca prison gang, Ricardo Valles de la Rosa, 45, in connection with the killing of a pregnant American consulate worker and her husband. The husband of another consular employee was also killed and his two young children were wounded. The arrest of Mr. Valles de la Rosa, who has a long criminal history in Texas and is wanted on drug dealing charges there, comes after the Federal Bureau of Investigation swept through El Paso on March 18, arresting more than 100 members of the street gang and interrogating them about the killings. Mr. Valles de la Rosa was stopped in a car at an undisclosed location by Mexican soldiers at 6 a.m. on Friday. He has been held since then on a weapons-possession charge. The pregnant consulate employee, Lesley A. Enriquez, and her husband, Arthur H. Redelfs, had just left a birthday party with their 7-month-old daughter when they were attacked on March 13. A few minutes later, Jorge Alberto Salcido, the husband of a Mexican employee at the consulate, was also killed after leaving the same party.

The Barrio Azteca gang has its roots in Texas Prisons, but has operated on both sides of the border since the late 1990s. Its members sometimes hire themselves out to the Juárez drug cartel for assassinations and other jobs

, law enforcement officials say. Mr. Valles de la Rosa, a native of Juárez, is wanted in El Paso on a drug dealing charge, the El Paso Sheriff’s office said. He is also a prime suspect in Mexico for the murder last year of Marco Zapata Reyes, who was member of the rival gang Los Mexicles, the newspaper El Universal reported.