During an interview with a local TV station, Venezuelan Minister of Penitentiary Services Iris Varela confirmed the clashes happened at the Yare I prison in the country's Miranda state, saying the dead also included a family member of one of the prisoners.
Local media reports said most of those killed were inmates in a part of the facility known as "La fosa" (The Trench), where prisoners who can't pay monthly protection fees to the group in control are relegated.
The head of the non-governmental Venezuelan Prison Observatory, Humberto Prado, said 25 bodies were brought to the local morgue by early Monday morning while 40 others were treated for injuries in local hospitals.
The clashes erupted Sunday between 4 p.m. and 8 p.m. local time (20:30 Sunday to 00:30 Monday GMT) in the Yare I penitentiary, between two heavily armed rival gangs vying for control of the jail, said Varela, who vowed to punish those who were held accountable for causing the deaths and injuries at the prison.
About 20 incidents of fighting or rioting have taken place in prisons across Venezuela since last year, most of them are triggered off by conflicts between groups who control the facilities and other inmates.
The Ministry of Penitentiary Services has been created with the mission to resolve such conflicts by mediating and confiscating arms.