Mass graves were reportedly discovered in the Libyan town of Tarhuna. Government troops recently seized control of the area after the withdrawal of forces loyal to rebel warlord Khalifa Haftar.
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.
"International law requires that the authorities conduct prompt, effective and transparent investigations," said the UN mission.
The graves were found after the UN-recognized Government of National Accord (GNA) retook control of Tarhuna when military general-turned-warlord Khalifa Haftar's Libyan National Army (LNA) withdrew from the region.
About 160 bodies found were transferred from Tarhuna's public hospital to Tripoli and Misrata, the director of Tarhuna's hospital told news agency AFP. However, the GNA has not yet reported the official number of bodies found.
The GNA said the Justice Ministry had set up a committee to investigate the graves and identify victims.
Khalifa Haftar's forces last year launched an offensive to capture the capital city of Tripoli. Though he failed to conquer the entire city, he managed to take control of the Tripoli airport. Hifter is backed by Russia, Egypt and the United Arab Emirates. The conflict has left hundreds dead and forced 200,000 to flee their homes.
In recent weeks, forces loyal to the GNA recaptured territory in northwestern Libya, including the Tripoli airport, with the help of Turkish drones.
Haftar supports a rival government in Tobruk. In February, the UN-backed government suspended cease-fire talks in Geneva after Haftar's forces attacked key positions in the capital, including its port.
The US and EU have called for a cease-fire following Haftar's losses. However, the GNA intends to push forward towards Sirte, the last significant settlement before the boundary between western Libya and Haftar's stronghold in the east.