GENEVA, June 6 (Reuters) - About 14,000 Libyans and refugees languish in overcrowded prisons in Libya, marked by torture, deplorable conditions and a lack of due process, the United Nations said on Friday.
About half of the inmates "continue to be deprived of their liberty without regard for due process", many of them held since the 2011 conflict to overthrow former leader Muammar Gaddafi, U.N. human rights spokesman Rupert Colville told a briefing.
A further 7,000 refugees and migrants, many from the Middle East or sub-Saharan Africa who had travelled to Libya to try to reach Europe by sea, were also being detained, he said.
"Detention of refugees and migrants in Libya, instead of being an exceptional measure, as required under international law, is widespread and prolonged," Colville told Reuters.
"They 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."
Armed groups hold prisoners in separate detention facilities that should be brought under government control, Colville said, noting that the United Nations last October documented 27 deaths in custody suggesting that torture was the cause.
Libya is threatened with chaos, as government and parliament are unable to control militias, armed tribesmen and Islamists who helped overthrow Gaddafi but now defy state authority.
Irregular forces and Islamist militias have been fighting in the port city of Benghazi for three weeks, and more than 100 people have been killed in almost daily clashes, some involving helicopters or war planes and hitting residential areas.
"Hardly a week goes by without some assassination, armed groups of ambushing people and killing them, bombs and all the rest of it," Colville said.
"So it's a very alarming situation and it just continues all the time and seems if anything to be getting a bit worse."
The International Committee of the Red Cross suspended its operations in Libya on Thursday after a Swiss staff member was shot dead by unknown gunmen in Sirte.
Colville condemned the killing, calling on authorities to launch "a prompt, impartial and independent investigation and ensure that those found responsible are brought to justice".
"This is fundamental to ensuring that the rule of law is upheld and the culture of impunity is not allowed to grow even worse," he said.
(Reporting by Stephanie Nebehay; Editing by Louise Ireland)