ROME (Reuters) - A video appearing to show men auctioned as slaves in Tripoli has put a long history of abuses against refugees and migrants there on the international agenda, the United Nations refugee chief said on Thursday.

U.N. High Commissioner for Refugees (UNHCR) chief Filippo Grandi speaks with Reuters journalist in Rome, Italy, November 30, 2017. REUTERS/Stefano Rellandini

Grainy footage broadcast by CNN earlier this month appeared to show an auction of men offered as labourers to Libyan buyers for $400, prompting outrage and anger in Europe and Africa.

But migrants who reach Europe by sea have been telling stories of being kidnapped, imprisoned and forced to work for no pay for years.

“Unfortunately, the horrifying abuses which that video made evident, made obvious to the whole world, are not new,” Filippo Grandi told Reuters in Rome. “The merit of that video is that it has now put the issue on the international agenda.”

Some African countries recalled their ambassadors after the video was broadcast, and the U.N. Security Council held a special session to discuss the issue after French President Emmanuel Macron railed against “crimes against humanity” in Libya.

Partly in response to the video, European and African leaders meeting in Abidjan on Thursday agreed to a plan to cooperate to fight smuggling and seek to ease a human rights disaster in Libya.

“We’ve heard finally authorities - Libyan authorities, the international community - talk about practical measures and how to respond to those abuses, to try to stop them, and to try to find solutions for the people affected by them,” Grandi said.

More than half a million migrants largely from war zones in the Middle East and Africa have reached Europe by sea after setting off from the Libyan coast over the past four years, bringing with them numerous tales of abuse.

The International Organisation for Migration (IOM) said in April it had been told of “slave market conditions” in Libya and Niger.

A Nigerian man, John Osifo, told Reuters in May after he was rescued at sea by a humanitarian ship that he had been forced into hard labor, treated like an animal, and beaten with a metal pipe.

“For Libyans, our black skin is like diamonds,” Nicky Yong from Cameroon said. He watched two men barter for him when he was sold to work as a “builder”, he said.

TRANSIT CENTER

After months of negotiations, Libya’s U.N.-backed government in Tripoli agreed this week to open a transit center for vulnerable refugees, which will be used to house people before they can be resettled or evacuated to another country.

The U.N. told Reuters in September it hoped to open the center, where refugees can be protected from smugglers and criminals, early next year.

Grandi said that more such facilities will be needed, and that the United Nations High Commissioner for Refugees (UNHCR) needs to have better access to the detention centers currently being run by the Tripoli government.

“We will need to create probably more (transit) facilities,” Grandi said. “We will also need to have more access... to the detention centers to do the work that we want to do,” Grandi said.

William Lacy Swing, head of the IOM, told the U.N. Security Council on Tuesday that it was working with partners to try to empty the detention centers in Libya. Some 30 centers, condemned as inhumane by rights groups, are estimated to hold 15,000-20,000 migrants.

Hundreds of thousands of other migrants are estimated to be in Libya, and many of them are being held by smugglers under lock-and-key in a country consumed by factional violence since strong man Muammar Gaddafi was ousted six years ago.