Authorities in Nigeria say as many as 40,000 girls and women have been trafficked to nearby West African countries to serve as sex workers.
Simon Egede said Wednesday that investigators from his National Agency for Prohibition of Traffic in Persons found slave camps full of Nigerian women and girls in Mali, Ivory Coast, Burkina Faso, Niger, Libya, Morocco and Cape Verde.
He says he estimates that there are between 20,000 and 40,000 victims.
He says Malian officials are planning arrests soon, and that Nigerian authorities are working to shut down operations elsewhere and prosecute the Nigerian traffickers.
Human Rights Watch reported earlier this year that many Nigerian teenage girls, some as young as 15, had been trafficked to Ivory Coast.