Tarek William Saab identified the two men as a lieutenant and a sergeant in Venezuela's General Directorate of Military Intelligence.

A Caracas court charged the men, Lieutenant Ascanio Tarascio and Sergeant Estiben Zarate, with homicide and ordered they be held in preventive detention.

UN rights chief Michelle Bachelet said earlier she was "shocked" by the death of retired officer Rafael Acosta Arevalo, adding weight to claims by the United States and the opposition that he may have been tortured.

The officer "died while in the custody of Maduro's thugs and their Cuban advisers," the US State Department said in a statement on Sunday.

Acosta was part of a group of 13 people arrested for alleged involvement in a failed "coup d'etat" against Maduro, which the government has tied to opposition leader Juan Guaido.

Maduro's government has claimed the coup was to have taken place on June 23 and 24 and involved the assassination of the president and several other senior officials.

Acosta was detained on June 21 and his whereabouts were unknown before he was brought before a military tribunal on June 28 and accused with others of plotting to overthrow and assassinate Maduro.

According to his lawyer, the naval officer appeared in court in a wheelchair, unable to speak and showing signs of having been tortured, a statement from the UN Commissioner for Human Rights said.

The judge sent him to a military hospital where he died the next day.

"I am shocked by the alleged torture of... Acosta Arevalo, and that his treatment in custody may have been the cause of his death," Bachelet said in a statement Monday.

"I urge the authorities to conduct an in-depth investigation -- including an autopsy meeting international standards -- that is both independent and transparent," she said.

Venezuela's defense ministry said in a statement that Acosta had "fainted" during the court hearing and that the judge ordered him transferred to a hospital, "where he died."

Saab had pledged "an objective, independent and impartial investigation" into the death.

Bachelet, a former Chilean president, visited Caracas last week and called for the release of imprisoned political opponents in the country, which NGO Foro Penal says number close to 800.