"Tackling impunity would not only end the suffering of tens of thousands of migrant and refugee women, men and children seeking a better life, but also undercut the parallel illicit economy built on the abuse and exploitation of migrants and refugees," it said.
It said migrants were subject to "unimaginable horrors" from the moment they entered Libya through their stay and attempts to cross the Mediterranean Sea to Europe. They included killings, torture, arbitrary detention, gang rape, slavery, forced labor and extortion.
READ MORE: US Commander Predicts US Mission Return to Libya 6 Years After Benghazi Attack
The UN High Commissioner for Refugees had registered 53,285 refugees and asylum seekers in the country as of September 2018, but their actual number is believed to be much higher, with 4,000 to 7,000 people being held at detention centers at any given time.