The death toll of a mass overdose at a Venezuelan prison last month has risen from 35 to 48, officials said on Thursday.

Inmates at the David Viloria penitentiary center in the western Venezuelan state of Lara raided the prison's infirmary on November 24, after a protest for better living conditions spiraled out of control.

Forty-eight of 148 intoxicated prisoners later died after consuming a deadly concoction of pure alcohol and drugs used to treat a number of ailments including diabetes, epilepsy and high blood pressure.

Speculation over events

November's incident has thrown the South American country's notoriously turbulent prisons back into the spotlight. A bloody riot at that same prison last year claimed over 50 lives. According to the Venezuelan Prison Observatory, most of the country's prisons are run by armed inmates, with the security forces having little or no control.

There has been no independent confirmation of what happened during the overdose incident, and families and human rights groups have cast doubt over the official version.

Testimonies collected from relatives of prisoners by the Venezuelan Observatory of Prisons say the inmates were poisoned by water and food brought in from outside.

On Thursday, the Inter-American Commission on Human Rights urged the Venezuelan government to pursue further investigation.

ksb/mg (AP, Reuters)