All sides in Libya's conflict, including Russian mercenaries, have committed violations that may include war crimes, UN human rights investigators say, adding that they had drawn up a confidential list of suspects.
Libya has been in turmoil for a decade, with the last several years seeing war between forces backing rival governments based in the east and west, supported by regional powers, foreign fighters and mercenaries.
Russia, Egypt and the United Arab Emirates backed the eastern forces, while Turkey backed the government in the west.
"The investigations indicated that several parties to the conflicts violated (international humanitarian law) and potentially committed war crimes," the UN fact-finding mission led by Mohamed Auajjar said in a report.
The report specifically accused mercenaries from Wagner, a Russian security firm, of having shot prisoners. "There are thus reasonable grounds to believe that Wagner personnel may have committed the war crime of murder," it said.
Reuters was not immediately able to reach Wagner, and the secretive firm has not responded to questions about its activities in the past. When asked last year about allegations of Russian mercenary activity in Libya, President Vladimir Putin said that if any Russians are fighting there they do not represent the Russian state.
Major combat in Libya has been paused since last year after an advance on the capital by the eastern forces was pushed back in 2020, and both sides have accepted a ceasefire and unity interim government. An election is planned for December.
Libya's foreign minister said on Sunday that some foreign fighters had left the country as the unity government seeks to marshal international help to withdraw the rest.
Torture and other abuses perpetrated on a "daily basis" in Libyan prisons against detained migrants may amount to crimes against humanity, the independent experts said.
The UN investigators identified the suspected perpetrator of one of the worst abuses - killings carried out by an armed group in the city of Tarhouna with victims buried in mass graves - as Mohammed al-Kani, a commander they said was himself killed in July during a raid by the eastern-based Libyan National Army.
Kani's armed group had been fighting alongside the LNA for years and had found refuge in LNA-held territory after being driven from Tarhouna. Neither the LNA nor police in Benghazi had previously confirmed the killing of Kani. Reuters was not able to contact his representatives.
Drone strikes that killed at least 12 people including women and children in Qasr Bin Ghashir, south of Tripoli, in June 2020 as the LNA was retreating from its failed assault on the capital, were believed to have been carried out by forces supporting the then western-based government, the report said.