Four people were killed and six were injured in a prison riot, involving, inmates and security forces in a northern Mexican border state on Tuesday, authorities said.
Loud, sustained bursts of gunfire were heard from outside the prison which is located in Ciudad Victoria, the capital of Tamaulipas state in northeastern Mexico.
Luis Alberto Rodriguez, spokesman on security issues for Tamaulipas said that those killed in the violence that lasted several hours were two state police officers, one security guard and an inmate.
"Those number are preliminary because the operation continues, there are still state police inside the prison inspecting the dormitories," Rodriguez, added.
He said authorities had observed "rising tensions" between opposing gangs in the prison over recent days and had information that they were smuggling in weapons.
Rodriguez said that the inspection operation had turned up two high-calibre weapons and a regular firearm.
"An intervention was planned which consisted in bringing state police into the prison and having federals support from the outside," he said, adding that if authorities had not intervened the number of casualties would have been higher.
Tamaulipas, a Gulf coast state bordering Texas, has seen the some Mexico's worst drug violence in recent years. Turf wars between the rival Gulf Cartel and Zetas gangs have racked the state for years.