A prison riot left at least four police officers dead and six other people wounded on June 6 in the Mexican city of Victoria, in Tamaulipas state.

Reporte Directo, a Victoria-based news organization, reported that there was a four-hour shootout during the riot.

Reuters reported: “Turf wars between the rival Gulf Cartel and Zetas gangs have racked the state for years, and in recent years some of Mexico’s worst drug violence has hit Tamaulipas.”

Family members of inmates were also seen gathered outside the prison awaiting updates. At the time of publication, Reporte Directo said the situation was calm, but the police operation was ongoing.