The violence began Thursday when Los Chapos, members of the notorious Sinaloa cartel led by Joaquin “El Chapo” Guzman, clashed with the local group Los Mexicles, at a Juarez prison, Deputy Security Secretary Ricardo Mejia said. A riot then broke out, leaving two dead and four injured with bullet wounds, Mejia said, speaking alongside Mexican President Andrés Manuel López Obrador at a regular news conference. Another 16 were injured in the fighting, he said. Officials did not say what caused the collision. After the uprising, the Mexiclos stormed the city, authorities said, killing nine civilians. Among them were four employees of a radio station, including an announcer, Mejía said. “They attacked the civilian, innocent population as a kind of revenge,” López Obrador said. “It was not only the conflict between two groups, but it got to the point where they were shooting civilians, innocent people. That is the most unfortunate thing about this case.” Mejía said four MegaRadio employees live-streaming a promotional event outside a business were killed in the shooting. Across the city, department stores were also shot at and set on fire. FEMSA, the parent company of the Oxxo chain, said in a statement that one of its employees and a woman applying for a job were killed in the violence. Chihuahua state Attorney General Roberto Fierro Duarte said a boy wounded in a shooting at a convenience store later died in hospital, two women were killed in a fire at another gas station and two other men were shot elsewhere in the city. Fierro said 10 suspects were arrested. At about 1 a.m. Friday, six alleged Mexicles members were arrested by local police, with the help of the army and national guard, Mejía said. Ciudad Juarez has long had a reputation for violence. Gangs like those involved in the insurgency often serve as proxies and law enforcement for Mexico’s powerful drug cartels that aggressively control the border crossing routes they need to get their wares into the United States. While still high, killings in recent years have been much lower than they were more than a decade ago — about 1,400 last year compared with more than 3,600 in 2010 — according to data from Molly Molloy, a retired border specialist at the New Mexico State University Library. which has tracked the city’s homicide data for many years and publishes regular updates on its Frontera List. The violence came two days after drug cartel gunmen torched vehicles and businesses in the western states of Jalisco and Guanajuato in response to the arrest of a high-ranking cartel leader. López Obrador, popularly known as Amlo, came to power promising “hugs not bullets,” which he promised would reduce the country’s rising murder rates. But experts say the strategy has encouraged criminal groups to become more violent and expand territorial control across the country.