"The alternative cannot be to resign ourselves to the impossibility of managing migratory flows and hand human traffickers the keys to European democracies," Italian Interior Minister Marco Minniti said on Wednesday.

On Tuesday the United Nations lambasted the EU's policy – led by Italy – of helping the Libyan authorities intercept migrants trying to cross the Mediterranean and return them to "horrific" prisons in Libya.

The human rights issue "is, was and will be a question we will not relinquish, but we know that condemning [abuses] is not enough, we must act," Minniti said, without entering into details.

Libya has long been a major transit hub for migrants trying to reach Europe, and many of them have fallen prey to serious abuse in the country at the hands of traffickers and others.

"The suffering of migrants detained in Libya is an outrage to the conscience of humanity," the UN said.

But Italy's foreign ministry said that Rome had been calling "for months" for those involved "to multiply actions and efforts in Libya to ensure acceptable and dignified conditions" in detention centres.

The UN had criticised the international community for turning a blind eye to the horrors endured by migrants in Libya and said it should not pretend the situation could be remedied by improving detention conditions alone.

But Minniti said Italy was doing its part by supporting a project to relocate 1,000 of the most vulnerable migrants from Libya to third countries.

His comments to parliament followed heavy media coverage in Italy of a CNN undercover report on migrants being sold as slaves in Libya.

"These auctions are just a variation of the horror we know," former Italian foreign minister Emma Bonino said.

"Men, women and children enslaved, raped, beaten, piled on top of one another [in the centres]. All this has been known for a long time," she said.