Mexico City (CNN) -- At least 31 inmates were killed and 13 were injured when a riot broke out in a northern Mexican prison Wednesday, authorities said.
The fighting started when inmates from one area of the prison entered another area, breaking prison rules, Tamaulipas state officials said in a statement.
Inmates used homemade weapons in the riot, the statement said.
The fighting occurred in a prison in the coastal municipality of Altamira, Tamaulipas, located about 300 miles (480 kilometers) south of the Mexico-U.S. border.
Authorities have identified 13 suspects who they believe were involved, the statement said. An investigation was continuing Wednesday.
CNN's Eduardo Aragon contributed to this report.