A riot at a Venezuelan prison left 50 people dead and dozens injured, CNN affiliate Globovision reported, the latest in a series of violent incidents in the nation's crowded detention system.
Clashes erupted Friday after local media reported about a planned operation to disarm prisoners at the facility in Uribana, the prison ministry said in a statement.
Venezuela's top prison official said national guard troops entering the prison were met with violence.
The troops went in to disarm inmates in what has become a notoriously violent prison, according to Iris Varela, Venezuela's prison minister.
Violence surged inside the prison this week, she said, as rival gangs battled for control.
The ministry did not release the number of casualties, but Globovision said at least 50 were killed and 90 others injured.
"Once we have absolute control of the facilities, we will specify the causes of what happened, the toll of people affected and offer a detailed, objective and true report as the constitution ... requires," the prison ministry said in a statement.
The ministry accused Globovision of sparking Friday's clashes by reporting on the operation at the prison, which officials had planned to keep under wraps.
"We were surprised by the announcement of said inspection on the part of the private channel Globovision, social networks and the website of the El Impulso newspaper, which without any doubt was a detonator for the violence," it said.
A leading opposition politician described the government as "incapable and irresponsible" following the riots.
"How many dead are there already in the Uribana prison?" Henrique Capriles Radonski, former presidential candidate and the governor of Miranda state, posted on his official Twitter account. "Desperate family members are calling us!"
Venezuelan prisons, which have been the scenes of bloody clashes in the past, are overcrowded and flowing with weapons and drugs.
In August, more than 20 people were killed after two heavily-armed groups clashed at Yare I prison outside Caracas.
More than 300 inmates died in Venezuelan prisons in the first half of 2012, according to the nonprofit Venezuelan Prison Observatory.
Inmates' relatives have accused officials of abusing prisoners. Authorities have blamed prisoners for the violence.