(CNN) French President Emmanuel Macron called the sale of migrants at slave auctions in Libya "a crime against humanity" and vowed to press for sanctions.

France has requested an "urgent" meeting of the UN Security Council to discuss this treatment of migrants in Libya, Foreign Minister Jean-Yves Le Drian said. France will advocate for international sanctions against Libya if its justice system fails to act, he said.

Libyan authorities launched a formal investigation into the human slave auctions , which CNN revealed this month in exclusive reporting.

After obtaining footage of a human auction in Libya, a CNN team went to the country in October to investigate. It saw a dozen men sold at an auction outside of the capital, Tripoli -- some for as little as $400. The crew was told of auctions taking place at nine locations in the country.

If confirmed, the new footage "compounds the already unimaginable and inhumane horrors endured by migrants in Libya," the United Nations in Libya said Wednesday. Recently, the UN's International Organization for Migration has alerted the international community to cases where migrants were being sold between human trafficking gangs, the agency said in a statement.

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