CARACAS, Venezuela - Pressure is building on Venezuela's government to fully investigate a rising number of deaths at an overcrowded prison, with human rights activists questioning authorities' claim of a mass drug overdose by dozens of inmates who stormed an infirmary.

After days of conflicting reports from the government and family members, the depth of the tragedy at David Viloria prison in western Venezuela became clearer Friday when authorities confirmed that 35 inmates had died and said 20 of an additional 100 still being treated for intoxication were in comas.

The government has said the troubles at the prison began Monday with a hunger strike for better conditions. A group of violent inmates raided the prison infirmary and then guzzled down a deadly mix of pure alcohol with drugs used to treat diabetes, epilepsy and high blood pressure, officials say.

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William Ojeda of the ruling socialist party said Friday after visiting the jail that many of the intoxicated inmates were drug users suffering from withdrawal symptoms due to the prison's strict regimen of abstinence.

Prisoner rights activists have been skeptical of the official version. They say that as deplorable as Venezuela's jails are no inmates would voluntarily end their lives or poison themselves as a form of protest.

A relative of an inmate cries while waiting for information outside the David Viloria prison in Barquisimeto, Venezuela, Thursday, Nov. 27, 2014 AP / Dedwison Alvarez

The lack of information and access to the prison has added to the mystery, with family members wondering whether loved ones could have been poisoned to restore order.

"Counting the deaths now requires going to the morgue" because government information is so incomplete, said Ligia Bolivar, a human rights expert at Andres Bello Catholic University in Caracas.

President Nicolas Maduro has yet to comment on the incident in frequent television appearances this week even as calls for a thorough investigation have come from Roman Catholic Church leaders in Venezuela and from the United Nations human rights agency.

On Thursday, police arrested the jail's warden, Julio Cesar Perez, who is expected to be charged in connection with the deaths.

The government says the situation at the prison is under control after it called in the National Guard and transferred hundreds of inmates to other facilities. All prisoners' rights are being respected, said Ojeda, who is president of a congressional committee that oversees the penitentiary system.

Venezuela's prisons are among the world's most violent.

Overall, the country's 32 correction facilities are the fifth most-crowded in the world, housing almost three times their intended capacity, according to the London-based International Centre for Prison Studies. The prison population has doubled since 2008 as a result of rampant crime and stiffer mandatory sentences.

The David Viloria prison is named for a guard who was one of 58 people killed at the facility last year during the second-deadliest prison riot in Venezuela's history. The facility, previously called La Uribana, was built to hold no more than 850 inmates but was believed to be holding around 3,000 when the latest disturbances broke out

Last year, 506 inmates died in the country's jails, according to the Venezuelan Observatory of Prisons, a nongovernmental watchdog group.