The United States-based human rights group, Human Rights Watch, says Venezuela's crumbling and overcrowded jails are the most violent in the world, where only the fittest survive.

The group says more than three-hundred-and-thirty people were murdered inside the prisons last year.

And Human Rights Watch says the violence appears to be dramatically increasing, with inmates making knives and other weapons to defend themselves.

Guns and hand grenades have also been discovered.

The Venezuelan prison authorities have admitted that they've virtually lost control of the twenty-six-thousand prison population.

The BBC South America correspondent says a slow justice system means the majority of inmates are still waiting trial.