Geneva, Nov 14 (IANS/AKI) The UN human rights chief on Tuesday expressed dismay at a spike in the number of migrants held in horrific conditions at detention facilities in Libya, saying the European Unions support for Libyan Coast Guard intercepting and returning migrants in the Mediterranean was inhuman.

"The suffering of migrants detained in Libya is an outrage to the conscience of humanity," Zeid Raad al-Hussein said.

An already dire situation had now turned "catastrophic," he said.

"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," Hussein said.

"The detention system for migrants in Libya is broken beyond repair," Hussein said.

Some 19,900 people were being held in Libyan government facilities in early November, a sharp increase from about 7,000 in mid-September when authorities detained thousands of migrants after armed clashes in the trafficking hub of Sabratha, according to Libya's department for combatting illegal migration.

"The increasing interventions by the EU and its member states have done nothing so far to reduce the level of abuses suffered by migrants," said Hussein.

"Our monitoring, in fact, shows a fast deterioration in their situation in Libya."

From November 1-6, UN human rights monitors visited four DCIM facilities in Tripoli in the first week in November, and reported seeing thousands of emaciated and traumatised men, women and children locked up in insanitary, overcrowded hangars and lacking "the most basic necessities", Hussein said.

The monitors interviewed detainees who reported kidnappings, torture, rape and other sexual violence, forced labour, exploitation, severe beatings, starvation and other atrocities during their journeys through Libya.

Migrants were powerless to defend themselves from the abuse, which is often perpetrated by traffickers or smugglers, and they cannot challenge the legality of their detention or gain access to legal aid, Hussein noted.

"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 traumatized people from reaching Europe's shores," he said.

He urged Libyan authorities to actively stamp out human rights violations in government-controlled centres, to open all migrant centres in the country, free those who detained and bring to justice individuals suspected of committing crimes against migrants.

"Only alternatives to detention can save migrants' lives and physical security, preserve their dignity and protect them from further atrocities," he said.

Hussein also called for domestic laws and legal migration to ensure migrants' human rights are safeguarded.

The EU and Italy are providing assistance to the Libyan Coast Guard to intercept migrant boats in the Mediterranean, including in international waters, despite concerns raised by human rights groups that this will condemn more migrants to arbitrary and indefinite detention where they are at risk of abuse.