A United Nations report based on 1,300 first-hand accounts has detailed abuse by smugglers and traffickers against illegal immigrants detained in or passing through Libya between January 2017 and August 2017.

The report revealed Thursday that the "overwhelming majority" of women and older girls who passed through Libya as migrants had been gang-raped by traffickers or witnessed others taken away to be abused.

The report turned up "unimaginable horrors" among migrants who sought to reach Europe through Libya, according to the Office of the High Commissioner for Human Rights (OHCHR.)

""There have been a terrible litany of violations and abuses committed by armed groups, state officials, traffickers and smugglers. The violations include unlawful killings, torture, arbitrary detention, gang rape, slavery, forced labour and extortion." The report adds.

OHCHR explains that many illegal immigrants are held in unofficial and illegal centers run directly by armed groups or criminal gangs.

The Head of the UNSMIL, Ghassan Salame, was quoted as saying in Thursday's report that there is a local and international failure to handle this hidden human calamity that continues to take place in Libya.

Libya has been burdened with thousands of illegal migrants - mainly from African sub-Saharan countries - either detained while journeying to Europe on unseaworthy boats or inland aboard trucks coming from southern borders of the country.