Government troops recently seized control of the area after the withdrawal of forces loyal to rebel warlord Khalifa Hifter.
The United Nations mission in Libya (UNSMIL) on Thursday voiced "horror" over recent reports of eight mass graves discovered in and around the town of Tarhuna.
The graves were found after the UN-recognized Government of National Accord (GNA) retook control of Tarhuna when military general-turned-warlord Khalifa Hifter's Libyan National Army (LNA) withdrew from the region.
Khalifa Hifter's forces last year launched an offensive to capture the capital city of Tripoli.
In February, the UN-backed government suspended cease-fire talks in Geneva after Hifter's forces attacked key positions in the capital, including its port.
