Mahmoud al-Werfalli, the senior leader of Haftar’s forces, is seen reading the charges and carrying out an execution himself in a new video posted online on Sunday.
It is believed the executions were carried out on July 17.
On July 18, the United Nations called for Haftar’s Libyan National Army (LNA), which controls the eastern part of the country, to investigate summary executions of prisoners.
In May, Haftar rejected a resignation letter submitted by Werfalli calling him “one of the sincere fighters who has given a lot in the battlefields for years.”
Rival factions to meet
Reports of the executions come as the leaders of Libya’s rival factions are planning to meet in Paris on Tuesday to discuss a deal to end the political crisis
The talks between the head of the UN-backed government Prime Minister Fayez al-Serraj and Haftar are aimed at stabilising the oil-producing country, which has been mired in chaos and fighting since rebels toppled former leader Muammar Gaddafi in 2011.
Foreign governments are pushing the UN-backed political agreement that installed Serraj’s National Unity government, but Haftar, whose forces have gained ground in the east of the country, has refused to accept the government’s legitimacy.
The two rivals held talks in Abu Dhabi in May, the first in more than a year and a half.
General Haftar’s forces have gained control in much of Libya’s east, with backing from the United Arab Emirates and Egypt.
Libya: Renegade general Haftar declares victory in Benghazi