Human Rights Watch on Wednesday accused the military authorities in eastern Libya of executing at least 31 people since late August.
It said these were the first known executions in the country since 2010, and followed what it described as “grossly unfair” military trials.
In addition, the rights group said at least 50 other people held at Gernada military prison are at risk of execution at any moment by the Libyan Arab Armed Forces.
It said the army, led by General Khalifa Haftar, has been putting them to death after secret trials built on confessions allegedly extracted through torture.
Many of the men were arrested in the cities of Derna and Benghazi during the armed conflict between Haftar's forces and rival armed groups between 2014 and 2018.
Human Rights Watch has called on the army to immediately halt executions and impose a moratorium on the death penalty.
Libya has been beset by violence and instability since the overthrow of Muammar Gaddafi in 2011.
The country is now run by two governments, an internationally recognised one based in Tripoli in the west, and the rival administration in the east backed by Haftar.