DAKAR (Thomson Reuters Foundation) - A video appearing to show African migrants sold as slaves in Libya sparked a global outcry on Monday as protests erupted in Europe and Africa, while soccer stars to U.N. officials made impassioned pleas for the abuse to end.

Two young men stand in the dark as an auctioneer shouts out prices in the footage published by news network CNN last week, appearing to sell them for the equivalent of about $400 each.

Young African men bound for Europe are frequently caught in trafficking networks and sold for labor in Libya, where many migrants are detained, tortured, and even killed, according to the U.N. International Organization for Migration (IOM).

The video, which the Thomson Reuters Foundation could not independently verify, was the first footage of people being sold, said Mary Fitzgerald, an independent researcher on Libya.

Protesters gathered outside the Libyan embassies in Paris and in African capitals including Bamako, Mali and Conakry, Guinea over the weekend and on Monday, according to local news reports. A protest is planned in London later this week.

Singers and soccer stars added their voices, with Manchester United’s Paul Pogba, of Guinean descent, throwing up his hands in a protest symbol after scoring a goal on Saturday and posting a message for ‘those suffering slavery in Libya’ on Instagram.

“What are you waiting for to react and intervene???” wrote Ivorian reggae artist Alpha Blondy in a Facebook post addressed to African leaders.

Many Libyans used the hashtag #LibyansAgainstSlavery on Facebook and Twitter, expressing horror and disapproval.

“Those of us who work in Libya have known about this for some time, but the video really brought it to the world’s attention,” said Fitzgerald, an author of a book about Libya.

The president of the U.N. General Assembly said on Twitter he was “appalled” by the reports of slave auctions, and the African Union called for an immediate end to the practice.

Six years after the fall of Muammar Gaddafi, Libya is still a lawless state where armed groups compete for land and resources and people-smuggling networks operate with impunity.

“People are rightfully outraged, but don’t hold your breath that anything real is going to happen,” Human Rights Watch (HRW) researcher Hanan Salah told the Thomson Reuters Foundation.

At least 20,000 migrants are being detained in Libya, which is the main gateway for Africans to reach Europe, according to the IOM.