The confidential report sent to the UN Security Council also said the Islamic State group is seeking to join migrant smugglers in southern Libya after it was pushed out of Sirte in 2016.
"Human trafficking is on the rise in Libya, resulting in major human rights violations," said the 157-page report by the panel of experts, seen by AFP today.
The panel raised concern "over the possible use of state facilities and state funds by armed groups and traffickers to enhance their control of migration routes."
The fate of migrants has come under intense security since film footage emerged last year of Africans auctioned off as slaves in Libya, drawing outrage from African governments.
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The report cited accounts from Eritrean migrants who were arrested in 2016 in Tripoli by agents of a special force affiliated to Libya's interior ministry who handed them over to migrant smugglers "against payment".
Four Bangladeshi migrants arrested by the Special Deterrence Force (SDF) in Tripoli were held in a government detention center in 2015 even though they held valid work visas.
"The panel is assessing whether the SDF's leadership was aware of collusion and trafficking being conducted within its ranks," said the report.