A fire allegedly started during an attempted jailbreak from Venezuelan police holding cells which killed 68 people on Wednesday, the country's top prosecutor and an inmates' rights group said.
The blaze at the detention facility in Carabobo state is the latest in a series of deadly incidents in Venezuela's overcrowded jails.
"In light of the terrible events that took place in the Carabobo state police headquarters, where 68 people died in a presumed fire, we have appointed four prosecutors... to clarify these dramatic events," chief prosecutor Tarek William Saab said on Twitter.
Carlos Nieto, the head of Una Ventana a la Libertad (A Window on Freedom) said that "some burned to death and others asphyxiated" after setting fire to mattresses and stealing a guard's gun in an attempt to break out.
Among those who died were two women, that was thought to have been visiting the jail at the time of the incident, Nieto said.
Relatives, of those being kept in the detention centre, tried to force their way into Carabobo state police headquarters. After one officer was injured by a stone, the crowd was dispersed by police firing tear gas.
Venezuela's prisons suffer from dire overcrowding and a shortage of basic supplies, struggling under the deepening economic crisis that is gripping the once, very wealthy oil-producing country.
"All the police stations in Venezuela are facing similar or worse conditions of overcrowding, lack of food and disease," Nieto said.
The association said 65 people died last year in the holding cells due to violence, malnutrition or tuberculosis. Two weeks ago, 58 detainees escaped holding cells on Margarita Island, a favoured spot for tourists, when a hole opened up in their facility's wall. They were all soon recaptured.