A fire at Venezuela's central Tocuyito prison killed 17 people and injured 11 early on Monday, the state prosecutor said in a statement.
Eight women and nine men were killed by the fire at the prison in the state of Carabobo, the statement said. The cause of the blaze was being investigated but there was no immediate indication of how it started, it said.
Carlos Nieto, director of prison rights group Window To Freedom, said inmates told him an electrical fault had caused the fire.
"It was due to negligence by authorities in not having adequate prison conditions," Nieto said.
Prison authorities did not respond to requests for comment.
Jails in Venezuela are severely overcrowded, housing 55,000 inmates even though they are designed for around a third of that number, Nieto said.
Riots, breakouts and deaths are common. Jails are often run by heavily armed inmates who have easy access to drugs and cellphones.
In October, authorities relocated more than half Tocuyito's inmates, or just over 2,000 people.