The UN refugee agency said it was gravely concerned about deterioration in conditions for migrants in Libyan detention centres tha led to riots and hunger strikes.
Many migrants are taken to the centres after being intercepted by Libya’s EU-backed coastguard as they try to reach Europe by sea, a policy criticised by human rights groups.
An estimated 8,000 migrants are currently held in 18 detention centres linked to the internationally recognised government in Tripoli, according to UNHCR.
Those detained make up a small fraction of several hundred thousand migrants resident in Libya or passing through the North African country.
Humanitarian workers have limited access to the centres, which frequently open and close.
“In recent weeks, UNHCR witnessed a critical worsening in conditions in detention centres, due to increasing overcrowding and lack of basic living standards,” the agency said in a statement.
“As a consequence, riots and hunger strikes by refugees in detention centres take place, demanding a resolution to the bleak living conditions. This has led to a number of serious security incidents, where UNHCR front line staff are at physical risk.”
Libyan officials blame poor conditions at detention centres on a lack of resources and said migrants are detained for their own protection.
Departures of mainly sub-Saharan African migrants from Libya to Italy peaked between 2014-2017 as the country slid into turmoil following a NATO-backed uprising seven years ago.
Last summer smuggler networks were disrupted under pressure from Italy and Libya’s coastguard stepped up interceptions.
So far this year 12,174 migrants landed in Italy from Libya, nearly 87% fewer than the same period in 2017 according to Italian interior ministry statistics.
There are nearly 55,000 refugees and asylum seekers registered in Libya, where they face limited chances of resettlement, according to UNHCR.