Human Rights Watch said Wednesday that authorities from the internationally recognized government in Libya are responsible for forcing confessions, not providing medical care and denying due process to detainees.
The group issued a statement detailing the accusations based on what it said were visits to three detention centers in eastern Libya controlled by the army and interior ministry in January and April.
The sites in Benghazi and al-Bayda collectively held 450 detainees, HRW said, with about half reporting being tortured while in custody and all of them saying they were not allowed to talk to lawyers, go before a judge or be formally charged.
"The lack of central government authority has spawned a widespread breakdown in law and order and the virtual collapse of the justice system, resulting in arbitrary detentions," the group said.
Libya has been divided by a power struggle between the internationally recognized government based in Tobruk and the militant-led, self-declared government operating out of the capital, Tripoli.
HRW called on the Tobruk-based authorities to bring charges against the detainees and release those for whom there is no credible evidence they committed any crime.
The group also said it received allegations that militias opposed to the Tobruk government were operating "informal detention facilities" in Benghazi, but that HRW workers were unable to gain access to those sites.