The European Union's policy of helping the Libyan authorities intercept migrants trying to cross the Mediterranean and return them to "horrific" prisons in Libya is "inhuman", the United Nations said Tuesday.
"The suffering of migrants detained in Libya is an outrage to the conscience of humanity," the UN human rights chief Zeid Ra'ad Al Hussein said in a statement.
"The European Union's policy of assisting the Libyan Coast Guard to intercept and return migrants in the Mediterranean (is) inhuman," he said.
Chaos-ridden Libya has long been a major transit hub for migrants trying to reach Europe, and many of them have fallen prey to serious abuse there at the hands of traffickers and others.
Zeid warned Tuesday that "the detention system for migrants in Libya is broken beyond repair."
"The international community cannot continue to turn a blind eye to the unimaginable horrors endured by migrants in Libya, and pretend that the situation can be remedied only by improving conditions in detention."
According to Libya's Department of Combatting Illegal Migration (DCIM), 19,900 people were being held in facilities under its control in early November, up from about 7,000 in mid-September.
The increase came after authorities detained thousands of migrants previously held by smugglers in Libya's people-trafficking hub Sabratha, to the west of Tripoli.
Zeid said staff members had visited four DCIM facilities earlier this month and were "shocked" by what they saw.
There were "thousands of emaciated and traumatised men, women and children piled on top of each other, locked up in hangars with no access to the most basic necessities, and stripped of their human dignity," he said.
Migrants, including children, described horrific beatings by guards at detention centres, while many women said they faced rape and other sexual violence at the hands of smugglers and guards.
One woman told UN staff she was gang-raped by three men, including a DCIM guard, while another woman said four armed men gang-raped her during her journey, when she was pregnant.
"I bled profusely, and I think I lost the baby. I haven't seen a doctor yet," she said.
The UN urged Libyan authorities to take concrete steps to halt violations and abuses in the detention centres, and to stop detaining migrants.
"The increasing interventions of the EU and its member states have done nothing so far to reduce the level of abuses suffered by migrants," Zeid said, adding that instead there appeared to be "a fast deterioration in their situation in Libya."
Zeid's comments came after ministers from 13 European and African countries on Monday pledged to take steps to ease the crisis around the Mediterranean, especially to help improve conditions for migrants held in Libya.
At a meeting in Bern of the contact group on the crisis along the Central Mediterranean migration route, the ministers also reiterated a pledge to strengthen Libya's coast guard.
Italy, with the support of the EU, has since the summer been training the Libyan coast guard to intercept boats as part of a controversial deal that has seen migrant arrivals to Italy down nearly 70 percent since July.
Reacting to Zeid's charges, an EU spokesperson noted that Brussels was funding UN agencies on the ground in Libya working to protect migrants.
"We believe that the detention centres in Libya must be closed. The situation in these camps is unacceptable", the spokesperson said in a statement sent to AFP.
The EU wants to see that rescued migrants are brought "to reception centres that meet international humanitarian standards", the spokesman said, while at the same time improving the Libyan Coast Guard's capacity to prevent deaths at sea.
But the UN rights office criticised European countries for ignoring warnings that the deal with Libya could condemn more migrants to detention, exposing them to torture, rape, forced labour and extortion.
"We cannot be a silent witness to modern day slavery, rape and other sexual violence, and unlawful killings in the name of managing migration and preventing desperate and traumatised people from reaching Europe's shores," Zeid said.