Sub-Saharan African migrants are being sold for as little as $400 in auction houses around Libya, a CNN undercover investigation has revealed.

The American TV channel revealed the slave markets that have taken place around Libya including in western Libya, around the capital Tripoli and near the border with Tunisia but also in Ghadames, a town near the Algerian border.

With hidden cameras the reporters travelled to Libya where they were able to watch a live auction of human beings. “Does anyone need a digger? He digs, he is a big strong man, he will dig,” a salesman tells the audience. Buyers then raise their hands, raising the price, “500, 550, 600, 650 …”

After a few minutes the auction ends and the men are transferred to their new “masters”. In the space of seven minutes a dozen Nigerians were sold.

“Migrants are sold on the market as if they were a commodity,” the head of the International Organisation for Migration in Libya, Othman Belbeisi, explained earlier this year. “Trafficking in human beings is becoming more common among smugglers, whose networks are increasingly powerful in Libya,” he added.

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According to CNN, this state of human trafficking has developed following drastic measures taken by the Libyan coastguard to stem the phenomenon of migration, significantly reducing the crossings of the Mediterranean migrants. With hundreds of migrants stranded at their disposal, the smugglers have adopted various means to profit from them which include auctioning migrants as slaves.

About one to two markets are organised each month for the sale of slaves, CNN reports. The images were handed over to Libyan authorities who promised to launch an investigation.

First Lieutenant Naser Hazam of the government’s Anti-Illegal Immigration Agency in the capital Tripoli told CNN that he had not witnessed a slave auction but acknowledged that organised gangs are operating smuggling rings in the country.

“They fill a boat with 100 people, those people may or may not make it,” Hazam explained. “[The smuggler] does not care as long as he gets the money, and the migrant may get to Europe or die at sea.”

Migrants have regularly faced abuse in Libya where their money is taken by smugglers in return for space on dinghy boats where people often drown while attempting to cross the Mediterranean or they are forced to live in detention centres where they face torture and rape.