(CNN) Canada has announced it will take in 750 refugees from Libya, some rescued from migrant detention centers.

Immigration Minister Ahmed Hussen said in a statement that Canada had already resettled more than 150 people, with another 600 anticipated to arrive in the next two years.

Two years ago, CNN revealed video footage that showed migrants being sold into slavery in Libya, some for as little as $400 each. It caused an international outcry, with the UN Security Council condemning the sale of migrants as "heinous abuses of human rights."

Announcing Canada's move, Hussen said: "In 2017, the world was shocked to see the harrowing images of people being sold into slavery in Libya.

"In response to the situation, Canada was one of the few countries to step up to work with the UNHCR [the UN refugee agency] to resettle these refugees directly from Libya and offer them a new home in Canada."

He added that Canada would also resettle 100 refugees from Niger, rescued from Libyan migrant detention centers, including victims of human smuggling.

Vulnerable migrants

Libya is a major transit point for migrants from Africa on their way to Europe. But they are vulnerable to exploitation, and as well as being sold into slavery some have been abducted and tortured to extort a payment for their release.

There are an estimated 4,900 refugees and migrants still held in Libyan detention centers, including 3,600 in need of international protection, according to UNHCR.

"They're enduring nightmarish conditions," a spokesman for the agency told CNN.

"The use of detention is routine for people intercepted and rescued at sea, but there have been widespread reports of human rights violations, detainees being given insufficient food, insufficient access to healthcare, as well as allegations from former detainees of torture and sexual assault taking place."

Deadly crossing

Last year more than 2,000 migrants died attempting to cross the Mediterranean to Europe.

JUST WATCHED Rescued migrants tell of abuse in Libya Replay More Videos ... MUST WATCH Rescued migrants tell of abuse in Libya 02:53

But the number attempting the crossing has fallen dramatically.

Coastguard agency Frontex reported that last year, just over 23,000 irregular crossings were detected from Libya, Algeria or Tunisia to Italy, an 80% decrease compared to 2017.

Italy closed its ports to migrant boats in June last year.

UNHCR welcomed Canada's announcement, said the spokesman.

He added: "We're urging resettlement states to come forward and not only offer places for refugees to be evacuated outside Libya but also to accelerate these processes so that this can happen as urgently as possible."