A riot at a prison in the Mexican city of Monterrey involving inmates belonging to rival drug cartels has left at least 52 dead and 12 injured, just days before Pope Francis is due to visit another prison in northern Mexico, reports theguardian.Jaime Rodríguez, the governor of Nuevo León state, which encompasses Monterrey, confirmed the death toll on Friday morning and told reporters that the riot at the Topo Chico prison had begun shortly before midnight.“During the clash several prisoners set fire to the food storage and sleeping areas,” Rodríguez said. It was not immediately clear how the victims died but the governor said there had been no gunfire.Rodríguez said that one of the factions involved in the violence was led by a leader of the Zetas cartel, Juan Pedro Saldivar-Farías, known as “Z-27”. The leader of the other group, Jorge Iván Hernández, “El Credo”, was identified by Mexican media as a leader of the Gulf Cartel.Los Zetas, founded by a group of former special forces soldiers, were originally the Gulf Cartel’s enforcement wing, but turned on their former masters in 2010, triggering a vicious war for territory which has wrought havoc across north-eastern Mexico.Saldivar-Farías was a suspect in the 2010 murder of American David Hartley, who was reportedly killed while jet skiing on Falcon Lake, which straddles the US-Mexico border.Television images of the riot showed flames leaping from the prison. Families of the inmates gathered at the prison, demanding information about inmates and hurling stones at guards. Several told Foro TV they found out of about the disaster on social media.The riot was the latest demonstration of Mexican authorities’ failure to establish control inside their own correctional facilities.“They left (Topo Chico) in the control of organized crime,” said Father Robert Coogan, a prison chaplain in the norther city of Saltillo, who belongs to a ministry that provides services to inmates in northern Mexican states.The most recent report on prisons by the National Human Rights Commission (CNDH) found widespread evidence of “autogobierno” – or self-rule by inmates – and assigned the Topo Chico facility a score of 5.72 out of 10. The survey showed a deterioration in Nuevo León prisons over the past five years; only five of Mexico’s 32 states ranked worse.Managing prisons has proved difficult in Mexico as the inmate populations swell with detainees from the ongoing crackdown on organized crime and drug cartels. Overcrowding has aggravated existing problems of corruption and intimidation in the cell blocks: prisoners are forced to pay inflated prices for everything from protection to proper food to being marked present in roll calls.The CNDH report found the majority of Mexican state prisons suffered overcrowding and conditions of self-rule, while guards in one-third of the facilities lacked the proper training.Coogan said wardens sometimes tolerate self-rule as it creates as sense of order – to the point that Los Zetas, when allowed to control the prison he served in Saltillo, kept the facility clean, imposed discipline and forced men to attend classes to complete primary and secondary school education.The scandalous situation in Mexico’s prisons was exposed by cartel kingpin Joaquín “El Chapo” Guzmán tunneling out of a maximum security facility last July. Marines recaptured Guzmán in January, prompting President Enrique Peña Nieto to tell Mexicans they could “trust” their security institutions.Thursday’s violence was the latest in a long line of riots and violent clashes within the country’s prisons. In 2013, at least 13 people were killed and 65 injured in a riot, in the central Mexican state of San Luis Potosí. In 2012, at least 44 inmates died in a Nuevo León prison in a fight between members of the Zetas and the Gulf Cartel armed with makeshift knives, clubs and stones.The Topo Chico riot occurred on the eve of Pope Francis’s arrival in Mexico for a visit in which he is expected to address uncomfortable issues like insecurity and violence. He also plans visit a prison in Ciudad Juárez, where cartels once called the shots and more than 200 murders were committed in 2010.Prisons officials say the Cereso No 3 in Ciudad Juárez has improved markedly and recently received US certification. During a visit by the Guardian, however, prison officials only allowed inmates to be interviewed in the presence of guards.