GENEVA (Reuters) - The U.N. refugee agency on Wednesday welcomed a decision by Libya to open a transit center for unaccompanied children and other vulnerable refugees from among hundreds of thousands of migrants, and called on EU countries and others to accept them.

FILE PHOTO: Migrants arrive at a naval base after they were rescued by Libyan coastal guards in Tripoli, Libya November 25, 2017. REUTERS/Ismail Zitouny

Reports this month of white Libyan slave traders selling black African migrants at markets in Libya - a grim echo of the trans-Saharan slave trade in centuries past - have drawn worldwide horror and condemnation.

Hundreds of thousands of migrants have been crossing the Sahara and the Mediterranean to reach Europe through Libya in each of the past several years. Thousands die during crossing the desert and at sea. Many are now being held in camps in Libya in conditions rights groups describe as inhumane.

The International Organization for Migration (IOM) has flown 13,000 migrants from Libya back to their countries of origin this year under a voluntary repatriation program. But thousands of others who face war or persecution at home cannot be sent back safely.

The United Nations High Commissioner for Refugees has been seeking to open a refugee transit center in Tripoli to resettle or evacuate as many as 5,000 of the most vulnerable out of Libya each year.

“UNHCR...welcomes the decision by the Libyan authorities to set up a ‘transit and departure facility’ in Tripoli for people in need of international protection,” the Geneva-based agency said in a statement on Wednesday.

With support from the Italian government, the initiative will facilitate the transfer of thousands of vulnerable refugees to third countries, it said.

“But we now need EU member states and others to step up with offers of resettlement places and other solutions, including family reunification slots,” said Roberto Mignone, UNHCR Representative to Libya.

The goal is to speed up the process of securing places in third countries, particularly for unaccompanied and separated children and women at risk, it 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 of around 15,000 migrants.

Nigeria’s president said on Wednesday the government had started bringing stranded citizens home from Libya after the global outcry over reports that migrants there were being sold into slavery.