The sale of migrants into slavery in Libya may amount to crimes against humanity, the United Nations Security Council said on Thursday, voicing "grave concern" after footage appearing to show Africans being auctioned there sparked global outrage.

The 15-member council unanimously adopted a formal statement calling on Libyan authorities to investigate the reports of migrants being sold and bring the perpetrators to justice.

Libya's U.N.-backed government last month said it would take action after a video broadcast by CNN, which appeared to show the auction of African migrants as farmhands for $400, led to protests across Europe and Africa.