At least 19 inmates have been killed since Sunday in armed clashes among prisoners in Venezuela's El Rodeo prison, an official said on Tuesday.
There was "a regrettable situation that occurred Sunday in El Rodeo where 19 inmates lost their lives," interior minister Tareck El Aissami told reporters.
About 20 wounded inmates have been transferred to hospitals, he said.
It would be the deadliest prison uprising in Venezuela since 1999 when 27 inmates were killed in a confrontation with security forces, according to rights organisations.
Gunfire and explosions could be heard into the night yesterday at the prison in the northern state of Miranda, but El Aissami did not say whether the situation had been brought under control.
Inmates' family members gathered outside the prison anxiously awaiting news of the fate of loved ones.
Humberto Prado, director of the non-governmental Venezuelan Prison Observatory, said that El Rodeo was overcrowded with more than 3,500 inmates in a facility built for 750.
That reflects a national trend, with 44,500 prisoners in a penitentiary system built for 15,000. More than 300 inmates die in prison violence each year.
President Hugo Chavez recently created a ministry to oversee the nation's prisons and allocated nearly 100 million dollars to "humanise" conditions in them.