Three inmates were found dead at a prison in Acapulco, a resort city on Mexico's Pacific coast, prosecutors said.
The bodies were found on Monday and the cause of death is under investigation, the Guerrero state Attorney General's Office said in a statement.
The three men were beaten to death during a fight at the Las Cruces prison, media reports said, citing police and prison officials.
The bodies were found in the early morning hours on Monday, the AG's office said.
Two of the dead inmates were serving eight-year sentences for robbery, while the third had been sentenced to 35 years and eight months for manslaughter and battery.
The three men had been transferred to Las Cruces from the Tuxpan prison in Iguala, another city in Guerrero, the AG's office said.
Nine people died at the prison in Iguala in an attack staged by gunmen last wek. EFE