Fifteen people were killed and dozens of others injured during a brawl among rival groups of inmates at Palmasola prison in the eastern province of Santa Cruz, Bolivian police said Friday.
The fight broke out after midnight Thursday in the prison's maximum-security cellblock, police Maj. Alberto Aracena told a press conference in Santa Cruz city.
A gas cylinder exploded during the disturbance, causing a small fire.
"There are around 15 people who lost their lives," Aracena said, adding that prison authorities had regained control of the situation.
Bolivia's prisons suffer from severe overcrowding, due in part to a chronically backlogged court system.
Eighty-three percent of the country's more than 13,800 prisoners are awaiting trial.
President Evo Morales' administration implemented mass pardons at the end of last year in an attempt to ease the crowding and is now considering an even broader amnesty.
Bolivian penitentiaries are also holding some 2,100 children who live with their parents behind bars.
A program to remove the youngsters from prison got under way in June after officials reached an agreement with the inmate parents. EFE