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Some held signs reading, “Put an end to the slavery and concentration camps in Libya.” Others carried flags. Many chanted, “Free our brothers!”

In Paris, hundreds of protesters walked along the Champs Elysées and gathered in front of the Libyan embassy Saturday to protest ‘slave auctions’ in the North African country, CNN reports. The protests came after CNN released an exclusive investigative report on migrants being sold as unpaid laborers in at least nine auction locations across the country.

Take Action: Stand With Nadia: Call for ISIS to be Held to Account for the Rape and Murder of Yazidi Women

According to the New York Times, the protesters were “mostly young black people.”

"How can it be that in the 21st century, we're selling human beings like merchandise?" one woman told CNN. "I cannot get my head around that!"

FRANCE: Crowds gather in Paris to protest against the modern slave trade in Libya 🇫🇷 🇱🇾 pic.twitter.com/5JV360OAQr — HĪP MAGAZINE (@HIPWEEKLY) November 18, 2017

“We have to mobilize — we can’t let this kind of thing happen,” another protester told the French television station France 24.

Protests became heated Saturday evening, after some young people threw projectiles at French riot police, but only one person was arrested, according to Le Figaro.

Read More: Migrants Are Being Sold as Slaves for $400 in Libya, Report Reveals

In the wake of the CNN report, the African Union called on Libya to investigate slave markets — which had previously been reported by the International Organisation of Migration (IOM).

On Friday, the government of Libya announced it had launched a formal investigation into the allegations through its Anti-Illegal Immigration Agency, according to CNN.

"Priorities of the investigation are not only to convict those responsible for these inhumane acts, but also to identify the location of those who have been sold in order to bring them to safety and return them to their countries of origin," an agency official told the network.

Various African leaders, including the chairman of the African Union Commission, Moussa Faki Mahamat and President Alpha Conde of Guinea, denounced the practice.

Image: Darko Bandic/AP

“The Chairperson of the Commission calls for an immediate end to these practices and other criminal acts of human trafficking,” Mahamat wrote.

Global Citizen campaigns against modern slavery, and is calling on the United Nations to investigate sexual slavery by ISIS against the Yazidi minority in Iraq. You can take action on this issue here.

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Other public figures, including French soccer star Paul Pogba, actor Omar Sy, and former Miss France winner Sonia Rolland, also spoke out about the slave auctions in North Africa.

“While very happy to be back, my prayers go to those suffering slavery in #Libya," Pogba wrote on Instagram and Twitter. "May Allah be by your side and may this cruelty come to an end!"

According to the CNN report, human trafficking has been exacerbated by a “clampdown” by the Libyan coastguard on boats that smuggle migrants to Europe — leaving smugglers with a backlog of desperate, impoverished migrants that they in turn enslave and hold for ransom.

Image: Santi Palacios/AP

The United Nations has estimated that nearly 20,000 migrants are currently being held by smugglers and in official detention centers in Libya.

“We cannot be a silent witness to modern day slavery, rape and other sexual violence, and unlawful killings in the name of managing migration and preventing desperate and traumatized people from reaching Europe’s shores,” United Nations High Commissioner for Human Rights, Zeid Ra’ad al Hussein, said in a statement.