A fight among inmates at a prison holding alleged members of drug cartels has left at least 31 people dead authorities in México say.
Officials say prisoners attacked each other using makeshift knives and other weapons at the prison in the northern city of Altamira on Wednesday. Some 13 more prisoners were wounded in the brawl.
Police and soldiers surrounded the prison and eventually regained control, according to officials.
Many of the inmates are serving sentences on drug-related charges.
The prison lies in Tamaulipas state, where the rival Gulf and Zetas drug cartels are fighting a bloody turf war. The violence from the drug war often spreads into prisons.