A deadly clash between prison inmates and the Venezuelan National Guard has left 54 people dead and close to a hundred injured in one of the country's notoriously overcrowded jails.
The killings, which were sparked by an attempt to confiscate illegal weapons at Uribana prison, poses a major challenge for a government whose ailing leader, president Hugo Chávez has not been seen since he flew to Cuba six weeks ago for cancer surgery.
According to local media reports the search had been planned for 4am on Friday but the heavily-armed inmates resisted and engaged in a fierce gun battle with the armed soldiers.
After two days of sporadic shooting and reports of killings by inmates, the authorities were still struggling on Saturday to gain full control of the facility in the western city of Barquisimeto.
The director of the city's Central hospital, Dr. Ruy Medina, told news agency AFP that the facility had received close to 90 wounded men, all suffering from gun wounds.
The death toll, which is expected to rise further, makes the conflict one of the deadliest riots the country has seen in the last decade.
Television news bulletins showed relatives crowded outside the hospital and the prison in search of information.
Iris Varela, Venezuela's penitentiary services minister, said the decision to search and disarm the men had been taken after authorities learned that rival gangs were preparing to confront each other in order to seize control of the facility.
However, she said the element of surprise was lost because reporters gave advance warning of the weapons search.
"This Friday we were surprised by the information announced in (private television channel) Globovision, social network sites and the web page of El Impulso newspaper," said Varela, who called the reports an "obvious trigger for violence."
But civil rights activists said the inmates and their relatives had long anticipated the government's plan. The deeper problem, they said, was that authorities used a disproportionate amount of force in a prison that was already at breaking point.
Venezuela's jail system is among the most violent and overcrowded in the world. Originally built for 12,000 inmates, the country's 33 penitentiaries across house 47,000 people. Guards are notable by their absence, leaving gang bosses free to run lucrative drug dealing operations from their cells.
Guns and knives are widespread, as is murder. In 2011, non governmental groups and human rights watchdogs reported 560 people were killed in prison.
Uribana - one of the worst - is known for the weekly "coliseum" contests, where inmates fight scheduled battles as crowds of convicts cheer, jeer and film the bloodshed.
There have been riots in the past, but the botched disarmament operation comes as a politically sensitive time with Chávez out of the country and in uncertain health.
His stand-in, vice president Nicolas Maduro, was greeted with the news on his return from Chávez's bedside in Havana. He insisted the operation was an important step forward.
"This (disarment) plan has been carried out with patience so that jails are freed from the violence, the mafias, drugs and deaths that have plagued them for a long time", Maduro told the state channel, VTV.