Libyan authorities raided a secret prison in a southeastern city used by human traffickers and freed at least 156 African migrants.

It came as the U.N. migration agency said Monday more than 1,300 Europe-bound migrants returned over the past week to the conflict-stricken country.

The Kufra security bureau said the raid took place on Sunday after a migrant managed to escape a house-turned-prison last week and reported to authorities that he and other migrants were held and tortured by traffickers there.

The bureau said at least six traffickers were arrested and referred to prosecutors for further investigation. 

Usman Umar reports.