Amnesty International accused the pro-putschist General Khalifa Haftar's forces in Libya of committing war crimes in the country's east.
The elite force led by Saddam Haftar is aimed at "crushing any challenge" to his father's army, which controls "vast swathes of the divided country," Amnesty said as it launched a new report.
"An unrelenting crisis of impunity in Libya has enabled fighters of the Tariq Ben Zeyad armed group to commit war crimes, and other crimes under international law ," the rights group added.
Khalifa Haftar's self-styled Libyan Arab Armed Forces (LAAF) has become one of the most prominent groups in the oil-rich but war-ravaged North African country.
It rules over much of eastern and southern Libya, despite failing to seize the capital Tripoli in a year-long assault in 2019-2020.
Khalifa Haftar, once a candidate in planned post-conflict presidential elections that never took place, today backs an eastern-based government challenging that of Abdel Hamid Dbeibah in Tripoli.
Since 2016, the force led by Haftar's son Saddam "has terrorized people in areas under LAAF control, inflicting a catalog of horrors, including unlawful killings, torture... enforced disappearance, rape and other sexual violence," said Amnesty researcher Hussein Baoumi.
The Tariq Ben Zeyad force has "no fear of consequences," Baoumi charged.
He called for "a criminal investigation" into Saddam Haftar and his deputy, Omar Imraj.
Their group has forcibly removed "thousands of refugees and migrants" from southern Libya and has been involved in the forced displacement of "thousands of Libyan families" during Haftar's various military campaigns since 2019, Amnesty said.
In November, the International Criminal Court's Karim Khan — the first chief prosecutor to visit Libya in a decade — said he had urged Haftar senior to prevent crimes by his troops.
"Military commanders must prevent, must repress and must punish crimes when they emerge," Khan said at the time.
Meanwhile, Libyan authorities exhumed two bodies from a new mass grave south of the capital Tripoli on Monday.
In a statement, the General Authority for Research and Identification of Missing Persons said the two unidentified bodies were found in a grave in the town of Sog Al-Khamies, nearly 50 kilometers (31 miles) south of Tripoli.
The town was under the control of putschist Gen. Khalifa Haftar before he was defeated by Libyan government forces in June 2020, and was consequently forced to retract to his stronghold in Benghazi city in eastern Libya.
Discoveries of mass graves are common in war-torn Libya, especially in Tarhuna city, a former stronghold for Haftar.
According to Libyan official sources, Haftar's forces and affiliated militias committed war crimes and acts of genocide in the period between April 2019 and June 2020.