Ten prison inmates were confirm dead, after a riot erupted in at a jail in Venezuela left an NGO official reported.
At least four grenades were detonated in clashes that began Monday evening in the northwestern state of Zulia, said the NGO, a human rights group called Una Ventana a la Libertad.
Venezuelan authorities have not said anything about a toll from the rioting, which the NGO said broke out at a jail which serves as a holding pen at a regional police headquarters.
Prisoners set fire to one wing of the facility, it said.
It quoted local residents as saying explosions and then gunfire were heard starting late Monday, with the violence continuing overnight.
Zulia governor Omar Prieto said Monday that he is planning to close the detention center.
On December 23, an uprising at the jail left six people dead, the NGO said. One of those was shot by security forces, it added.
It said the jail holds about 1,000 inmates.
Venezuelan prisons suffer from severe overcrowding despite a 2011 plan to upgrade them.