It was the latest in a series of bloody riots over the past year in overcrowded prisons here, where guns and drugs abound and inmates control many aspects of prison life.
Newspapers reported that more than 50 people had been killed at the Uribana prison in Barquisimeto, a northwestern city, citing the director of a hospital where the wounded and the dead were taken. The reports said that more than 80 people had been injured.
The minister of prisons, Iris Varela, said the violence broke out Friday when National Guard troops entered the prison to conduct an inspection, with the aim of taking weapons away from prisoners and establishing order.
“There was a tragic situation of confusion that we lament very much,” Vice President Nicolás Maduro said on television early Saturday. Mr. Maduro spoke after returning to Venezuela from Cuba, where he had gone to visit the country’s ailing president, Hugo Chávez, who has been out of sight since undergoing surgery in Havana for cancer more than six weeks ago.
Mr. Maduro is running the country in Mr. Chávez’s absence.
He described the prison as one of the country’s most dangerous, and he promised an investigation. “The prisons must be governed by the law,” he said.
There were conflicting reports about the episode but it appeared that inmates had resisted efforts by the National Guard to enter areas of the prison. The local news media reports indicated that some of the inmate bosses, known as prans, had been killed in the raid. The reports said that most of the dead were prisoners.
Ms. Varela said that two days before the raid the authorities received information of an increase in violence inside the prison, involving a settling of scores between different factions vying for control.
At that point, she said, the decision was made to have the troops enter the prison.
But she said that word of the operation leaked out and that it was reported by a television station, Globovision, on the Web site of a local newspaper and on social networking sites.
She called the reports “a detonator of the violence” and blamed them for setting off the riot inside the prison.
Last August, 25 people were killed and dozens were wounded in gunfights between inmates battling for control of the Yare I prison south of Caracas, according the official reports.
Also last summer, 30 people were killed in a prison riot in Merida, in the Andes Mountains, according the Venezuela Prison Observatory, a nongovernmental watchdog group. Outside the prison on Saturday morning a few hundred people, including many anguished relatives of prisoners, waited for news. Some sang the national anthem and some held signs that said “We want peace” and “No more deaths.”
“This happens all the time and nothing changes,” said Yolanda Rodríguez, 57, who was waiting for information about her 24-year-old son, an inmate in the prison. “We know nothing about what’s happening inside.”
Girish Gupta contributed reporting from Barquisimeto, Venezuela.