Former minister arrested in 2017 as part of fraud probe at state oil company dies in state custody, prosecution says.

Nelson Martinez, a former Venezuelan oil minister imprisoned over corruption allegations, has died of health complications, according to the prosecutor’s office.

The chemist, who also served as president of state oil firm PDVSA and its United States subsidiary Citgo Petroleum, was arrested on November 30 last year as part of a sweeping fraud probe, four days after President Nicolas Maduro removed him from his position.

“Nelson Martinez was suffering from a serious chronic illness whose progression aggravated his condition and led to his death. Until the last moment … he received the required treatment and medical attention in a health center,” the prosecutor’s office said on Wednesday, denying that Martinez died in prison.

Martinez had been transferred to a military hospital from prison because of kidney problems, two sources familiar with the matter told Reuters news agency earlier. He had a heart attack while receiving dialysis, they said.

Rafael Ramirez, a former state oil firm chief and opponent of the country’s president, had earlier announced Martinez’s death and blamed Maduro.

“Nelson Martinez just died … kidnapped and abused for a year under the orders of Maduro, who knew of his chronic illness. They humiliated him and denied him his right to defense and to life. Maduro, YOU are responsible,” Ramirez wrote on Twitter.

Martinez at the swearing-in ceremony of the new board of directors of PDVSA in Caracas on January 31, 2017 [File: Marco Bello/Reuters]

Prosecutors accused both Martinez and Eulogio del Pino, another former oil minister and PDVSA president, of being part of a corruption network in the country’s oil sector, with Ramirez at the helm.

Ramirez was the president of PDVSA for a decade from 2004, a member of late President Hugo Chavez’s intimate inner circle. Until a falling out with Maduro last year, Ramirez had not been investigated and served as Venezuela’s ambassador to the United Nations.

Martinez was jailed after the country’s top prosecutor said he allowed a poor refinancing deal for Citgo to go ahead without government approval.

He had yet to appear before a judge at the time of his death, and the date for his preliminary hearing was pushed back several times, Reuters reported. His lawyers began asking authorities months ago for Martinez to be granted house arrest, citing his ill health, a source told the news agency.

Martinez started having health problems while leading Citgo, based in the US city of Houston. Maduro named him oil minister in January 2017, and he assumed the dual role of PDVSA president later that year, replacing del Pino, who is currently jailed.

He had joined PDVSA in 1980 and oversaw the company’s offices in Britain, Argentina and Ecuador before being tapped to lead Citgo.

Martinez is the latest in a series of people to die in Venezuelan custody.

In August, opposition councillor Fernando Alban died after falling from the 10th floor of Venezuela’s intelligence services headquarters in the capital, Caracas.

The government maintains it was a suicide, but Maduro’s critics claim he was tortured during interrogation and thrown from a window.

Another opposition leader, Carlos Andres Garcia, also died last September while in the custody of intelligence services.

According to human rights organisation Foro Penal, there are 288 “political prisoners” in Venezuela.