31 killed in Mexico prison unrest At least 31 people were killed and 13 wounded in a battle among inmates that broke out in a prison in the northern Mexican border state of Tamaulipas, the state government said. The fighting broke out in the Santa Amalia prison in the city of Altamira, a site designed to hold 2,000 inmates but which has a population of more than 3,000. Authorities regained control after police moved in, the statement read, adding that 13 inmates involved in the fight were detained. Federal police forces and soldiers earlier surrounded the prison, a federal source told AFP. The prison is located in an area where the rival Gulf and Zetas gangs have a strong presence, and many of the inmates are doing time on drug-related charges. Deadly riots and prison fights are common in Mexico's overcrowded prisons. Twenty inmates were killed and 12 wounded in a mid-October prison fight in a jail in the border town of Matamoros, just across from Brownsville, in the US state of Texas.