About 14,000 Libyans and refuges, most of them from Middle Eastern countries, now live in overcrowded prisons in Libya. A UN statement on Friday said the detainees are often tortured; suffer deplorable conditions; and lack of due process.
UN human rights spokesman Rupert Colville said that about half of the inmates "continue to be deprived of their liberty without regard for due process." He noted that many of them have been held since the 2011, when the former dictator, Muammar Gaddafi, was ousted.
Colville told Reuters that about 7,000 refugees and migrants, many of them from the Middle East or sub-Saharan Africa, who had travelled to Libya in an attempt to reach Europe by sea, were also being detained.
The UN official continued: "They [inmates] do not usually have the means to challenge their detention and are kept in extremely poor conditions, with chronic overcrowding and lack of basic sanitary conditions. They are also subject to ill-treatment and exploitation for labour."
He called on the armed groups holding prisoners in separate detention facilities to bring them under government control. He noted that the UN had documented 27 deaths in custody last October, expecting that torture was the cause of these deaths.
Meanwhile, Libyan troops led by renegade retired Colonel Khalifa Hafter have been waging an anti-government operation for over three weeks. His forces often use fighter jets and tanks to attack populated areas. It is believed they are responsible for the killing of at least 100 people.
On Thursday, a Swiss ICRC staff member was shot dead by unknown gunmen in Sirte. Colville condemned the killing and called on the authorities to launch "a prompt, impartial and independent investigation and ensure that those found responsible are brought to justice".
He reiterated that "this is fundamental to ensuring that the rule of law is upheld and the culture of impunity is not allowed to grow even worse."