Sixteen inmates were killed and five more were wounded in a fight that broke out in a prison in the northern Mexican state of Zacatecas, the state government said in a statement Tuesday evening.
Security will be boosted at prisons in the state after the incident in the Varonil prison, which broke out around 2:30 pm on Tuesday afternoon, the government said.
An inmate was arrested with a firearm, and three more guns were found in the prison, as well as various knives.
The government has launched in an investigation to determine those responsible for the fight and how the weapons entered the prison, according to the statement.
The incident marks the latest blow to the security track record of Mexican President Andres Manuel Lopez Obrador, who has struggled to combat rising violence in the country.