More than 20 people were killed in the latest outbreak of violence in Venezuela's overcrowded prisons as heavily armed gangs fought for control of a prison near Caracas, authorities said Monday.

Iris Varela, the minister for prison affairs, told state-run media that the clashes erupted Sunday in the Yare I penitentiary, instigated by inmates "who want to maintain control through force."

"There are more than 20 (dead) and a family member of one of the prisoners also lost their life," she told state television network VTV.

VTV reported that there were people injured as well, but the government provided no details.

Local news reports said several hundred family members were visiting inmates at the prison when the violence broke out.

Varela blamed it on a confrontation between two "heavily armed groups" within the prison.

Local news reports said it may have been started by prisoners who had been transferred to Yare I from La Planta, a notoriously violent and overcrowded prison in Caracas that was closed after a violent, weeks-long uprising in May.

Stray gunfire in that confrontation killed a man in a nearby apartment building.

"Those responsible for the deaths within the prisons must answer for them," Varela said.

The government does not issue regular reports on conditions in Venezuelan prisons and does not confirm most violent incidents. In June, it fined a private television network $2.4 million for its coverage of bloody prison uprising in 2011.

Human rights groups say that in the year since President Hugo Chavez put Varela in charge of a newly created ministry of prison affairs, more than 500 inmates have been killed in prison violence and another 1,200 injured.

The Venezuelan Prison Observatory, a non-governmental group, said more than 300 inmates have died in the nation's overcrowded prisons during the first half of the year.

In July, 28 prisoners were killed and 17 injured in a prison uprising in the western city of Merida that took authorities three weeks to bring under control.

An operation to retake the El Rodeo prison, on the outskirts of Caracas, in June 2011 left 25 people dead, and some of the inmates escaped.

After that debacle, Chavez gave Varela the task of overhauling a prison system that has 50,000 inmates crammed in facilities built to hold 14,000 people.

Experts say the country's prisons remain a cauldron of violence, ruled from within by gangs with easy access to weapons and beyond the control of corrupt or ineffectual guards.

The latest outbreak of violence comes amid a presidential election campaign, and opposition candidate Henrique Capriles has taken aim at Chavez in the past over his government's handling of the prisons.