In its final report, the UN Independent Fact-Finding Mission on Libya concluded that there were "grounds to believe a wide array of war crimes and crimes against humanity have been committed by state security forces and armed militia groups."
"Migrants, in particular, have been targeted and there is overwhelming evidence that they have been systematically tortured" in detention centers, it said.
The probe voiced alarm at the deteriorating human rights situation in the conflict-torn North African country, warning that the European Union was supporting some of the organizations perpetrating abuses against migrants.
The mission's chairman Mohamed Auajjar said investigators found crimes in detention centers under the control of Libya's Directorate for Combating Illegal Migration (DCMI) and the country's coast guard.
"These entities receive technical, logistic and monetary support from the European Union and its member states" for the interception and return of migrants, the former Moroccan justice minister said.
Beyani added it was "clear that the DCIM has responsibility for multitudes of crimes against humanity in the detention centers that they run. The support given to them by the EU has facilitated this."
"We're not saying that the EU and its member states have committed these crimes," investigator Chaloka Beyani told reporters, adding though that "the support given has aided and abetted the commission of the crimes."
The group's report said there were reasonable grounds to believe that sexual slavery, a crime against humanity, was being committed against migrants.
Mission member Tracy Robinson said they also uncovered slavery in general.
"We have found instances of enslavement of persons who have been traded to outside entities to perform various services, but also sexual slavery of women in and around detention centers," she said.
The investigators voiced concern about the deprivation of liberty of Libyans and migrants throughout the country, in what they said could also amount to crimes against humanity.
They found numerous cases of "arbitrary detention, murder, torture, rape, enslavement, sexual slavery, extrajudicial killing and enforced disappearance, confirming their widespread practice in Libya".
Nearly all the survivors interviewed did not lodge official complaints out of fear of reprisals and a lack of confidence in the justice system.
The probe said it was deeply concerned at the deteriorating human rights situation in the conflict-torn North African country.
The three-member panel said there was a broad effort by the authorities in Libya to repress dissent by civil society.
The investigation found that Libyan authorities, notably the security sectors, were curtailing the rights to assembly, association, expression, and belief in order to ensure obedience, entrench self-serving values and norms, and punish criticism against authorities and their leadership.
The United Nations' Human Rights Council set up the fact-finding mission in 2020 to investigate violations and abuses of human rights from 2016 onwards.
The report was the mission's final update before its mandate expires.
It intends to share its closing findings with the International Criminal Court, including the names of individuals who could be held responsible for abuses.
Auajjar said Libyans and migrants were hoping the world would pay attention to the violations in the country.
"They are looking forward to the end of this nightmare," he said.
This report was sourced from Reuters and Agence France-Presse.
