Opposition leader Henrique Capriles condemned the government's handling of what he and many other critics call a growing crisis in the country's prisons.
"Our country's prisons are an example of the incapacity of this government and its leaders. They never solved the problem," Capriles said on his Twitter account. "How many more deaths do there have to be in the prisons for the government to acknowledge its failure and make changes?"
Venezuela currently has 33 prisons built to hold about 12,000 inmates, but officials have said the prisons' population is about 47,000.
The Venezuelan Prisons Observatory, a watchdog group, said in a statement that in 2007 the Costa Rica-based Inter-American Court of Human Rights had ordered the government to seize weapons that inmates had in their possession at Uribana prison and to take measures to avoid deaths in the facility. The group called for the government to release a list with the names of the dead and wounded in Friday's violence, as well as details about weapons seized in the search.
"No one doubts that inspections are necessary procedures to guarantee prison conditions in line with international standards, but they can't be carried out with the warlike attitude as (authorities) have done it," said Humberto Prado, an activist who leads the prison watchdog group.
"It's clear that the inspection wasn't coordinated or put into practice as it should have been. It was evidently a disproportionate use of force," Prado told the AP.
His group says Uribana prison was built to hold up to 850 inmates but currently has about 1,400.
Similar though less deadly clashes have flared repeatedly during the past few years.
In April and May, a prison uprising in La Planta prison in Caracas blocked authorities from going inside for nearly three weeks. One prisoner was killed and five people were wounded, including two National Guard soldiers and three inmates.
Two months later, another riot broke out at a penitentiary in Merida, and the Venezuelan Prisons Observatory reported 30 killed.
In August, 25 people were killed and 43 wounded when two groups of inmates fought a gunbattle inside Yare I prison south of Caracas.
Chavez's government previously pledged improvements to the prison system, but opponents and activists say the government hasn't made progress.
Varela, the prisons minister, said news media including Globovision and a local newspaper had run reports on the inspection by authorities, which she said had in fact been a "trigger for the violence."
Prado denied that, saying: "The problem isn't the work of the media. The problem is that the government hasn't disarmed the prison population."
Associated Press writers Vivian Sequera and Camilo Hernandez in Bogota, Colombia, and Fabiola Sanchez in Caracas contributed to this report.