Known by nicknames like "the Hyena" and "Jackal," Menendez ran the infamous La Perla concentration camp, where thousands of opponents of the 1976-1983 military regime were tortured. Executions were routine at the site, surviving witnesses said.

Some 30,000 people disappeared -- presumably killed -- under Argentina's military regime, according to human rights groups.

Menendez headed the III Army Corps based in the industrial city of Cordoba, Argentina's second most populous city and at the time a center of labor unrest.

The late general was so hardlined he dismissed other generals like the late dictator Jorge Rafael Videla as "soft" on the opposition.

"There was never any illegal repression," he told judges at one of his trials, showing no sign of remorse for his crimes.

Menendez and other regime officials accused of human rights violations faced a wave of lawsuits when a blanket amnesty for dictatorship-era officials was fully rescinded in 2005.

At the time of his death, Menendez had been sentenced to prison in 14 cases -- 13 of them to life behind bars -- and awaited the start of a 15th trial.

Telam reported that Menendez died of liver disease at a Cordoba military hospital.

"Unlike his victims, we know the time and place of his death, and his family could bid him farewell," the group HIJOS, representing children of dictatorship-era victims, said in a social media posting.

HIJOS noted that Menendez had been sentenced to a life in a common prison, "the only place for a supporter of genocide."