Police in Argentina say at least 32 prisoners have been killed in fires set by rioting inmates at a jail in Magdalena, south of Buenos Aires.
Authorities say most of the victims suffocated in smoke from mattresses and other items set ablaze after a fight broke out late Saturday.
Initial reports said the prisoners had been demanding longer visiting hours for relatives. But the justice minister of Buenos Aires province (Eduardo Di Rocco) said the disturbances were a result of prisoner infighting.
Authorities re-took control of the prison Sunday morning.
Hundreds of relatives came to visit inmates on Sunday, Argentina's Mother's Day, and instead waited outside the prison to learn the fate of their loved ones.
This was the worst of several violent outbreaks in Argentina's prisons this year.