One of the most notorious torturers of Argentina's former military dictatorship has died in prison at the age of 93.

The former deputy chief of police for the province of Buenos Aires, Miguel Etchecolatz, died of heart failure in hospital on Saturday, human rights organizations said.

According to media reports, Etchecolatz had been transferred to the clinic a few days earlier.

He was sentenced to nine life sentences in a series of trials, most recently last May.

During Argentina's military dictatorship from 1976 to 1983, Etchecolatz ran 21 secret prisons where thousands of people were tortured and killed.

One of the commandos he commanded was responsible for the kidnapping of a group of students between the ages of 14 and 17 in September 1976.

Only four of the students survived.

"Because of my job, it was my duty to kill, and I would do it again," Etchecolatz testified in one of his numerous trials.