Human Rights Watch reported last month Libya hasn't been able to establish a functioning justice system since the collapse of Col. Moammar Gadhafi's regime in 2011.
HRW's director of Middle East and North African programs, Joe Stork, said the government hasn't prosecuted anyone for a string of political assassinations since civil war ended in late 2011.
Tarek Mitri, U.N. special envoy for Libya, reported to the Security Council he was concerned by the thousands of conflict-related detainees held in the country.
"While the Ministry of Justice has reported a reduction in complaints, reports of deaths in custody torture and other forms of ill-treatment continue to be a source of concern," he said in his report Monday.
Libya plans to put Saif al-Islam, Gadhafi's son, on trial for war crimes committed during the civil war. Former Minister of Information Ahmed Ibrahim was sentenced to death in July for his role in the violence.
Mitri said Libya's justice system will be put to the test in the coming months.
"The prevailing security situation in the country and the continuing attacks on judges, lawyers and courthouses continue to present a formidable challenge to the authorities," he said.