BARQUISIMETO, Venezuela: Riot police squads worked Sunday to establish full control over a prison in northwestern Venezuela, where a riot has left at least 61 inmates dead and twice as many injured.

Prisons Minister Iris Varela admitted to reporters Saturday that the government "was not in control of all of the area of the Uribana penitentiary" in Lara state.

Security forces were currently working "to remove inmates from the heart of the jail," she said, adding that the rioters and other inmates would be moved to other prisons around the country.

Meanwhile, relatives of inmates missing after the deadly violence were desperately seeking news of their loved ones.

"I don't know if my son is alive or dead behind those big doors," said Elvira Rodriguez, weeping and waiting for her son Joseph, who has spent two years awaiting trial for kidnapping. "I have looked for him in all the hospitals."

Most of those killed in the clashes between prison gangs and security guards at the Uribana facility on Friday were shot by assault weapons. Antonio Maria Pineda Hospital director Ruy Medina said in an updated toll said another 120 people were wounded.

National Guard troops earlier surrounded the Uribana prison as inmates in bloody clothes were taken out of the building, as distraught relatives behind the barriers waited for news. Dozens more lined up waiting for death certificates.

Carmen Garcia was seeking word on her son Edilso Rodriguez, who had been brought back to the prison after being treated in hospital for a bullet wound.

"We just cannot find anybody who will give us an explanation," said the woman of about 50, who was among about 200 relatives.

"It was like a war movie here -- with tanks rolling and shooting and too much smoke," she said.

Vice President Nicolas Maduro, just back in the country after visiting President Hugo Chavez in Cuba, called the riot "regrettable" and "tragic," and said an investigation had been launched.

The Uribana prison is believed to hold about 2,500 inmates.

National Guard troops moved inside the facility in a bid to completely put down the uprising, law enforcement sources said.

Opposition parties immediately accused the government of exercising lax control over the prison system.

"Who will they blame for this massacre this time around?" opposition leader and former presidential candidate Henrique Capriles said on Twitter, calling the government "incapable and irresponsible."

Humberto Prado, head of the non-governmental Venezuelan Prison Monitoring Organization, said the government "had failed to take responsibility for the events" and instead was "piling blame on the media."

Venezuela is notorious for the poor state of its prisons, which suffer from some of the most staggeringly high levels of overcrowding in Latin America.

Originally built to house 14,000 inmates, the country's prisons now hold almost 50,000 people, often with low sanitary standards and high levels of violence.

In August 2012, at least 25 people were killed and 43 wounded during a clash between rival gangs in Yare I prison near Caracas. In June 2011, dozens died in a riot that erupted at El Rodeo prison.