Traffickers smuggling migrants across the Mediterranean are more likely to lock Africans, including women and children, into packed boat holds than Syrians and others from the Middle East, an official who interviewed survivors said on Friday.
Up to 900 people are feared to have drowned last weekend when their crowded vessel capsized as it headed to Europe from Libya, with many victims trapped below deck.
Itayi Viriri, spokesman for the International Organization for Migration (IOM), said shocking testimonies from migrants show that smugglers' treatment of sub-Saharan Africans is especially "inhumane and horrific".
Viriri, who met survivors of the latest tragedy in the Sicilian port of Catania this week, said migrants arriving by sea reported being beaten up, robbed of their savings, deprived of food and forced to drink filthy brown water.
Middle Eastern nationals receive preferential treatment, apparently because they pay more, Viriri added.
"The reality is that where there is a multiple-deck vessel those who pay less -- who usually are the sub-Saharan Africans -- are in the hold which is sometimes closed off.
"When a vessel capsizes those who survive are usually the ones at the top. The ones inside the hold, (often) children and women, are the ones who do not make it."
Around 2,000 migrants have died at sea this year trying to reach European shores, but Sunday's sinking is thought to be the deadliest on record.
The IOM said traffickers were exploiting the lawlessness in Libya from where most boats depart.
Viriri said migrants can be kept in holding houses for weeks or months waiting for a boat to be ready.
"One of the gentlemen we spoke to told of repeated beatings, people being asked to hand over money even though they'd already paid, and ... (people being) mugged, robbed.
"One man said he had to raise his $600 passage fee three times over -- twice that money was stolen from him."
Some migrants are forced onto rickety, overcrowded boats even if they change their minds, Viriri said.
The IOM welcomed a European Union plan to triple the size of its naval search mission in the Mediterranean following an emergency EU summit on Thursday.
But it said Europe must do more to increase resettlement options for those fleeing conflict so that they do not have to resort to traffickers.
Viriri said EU countries should resettle at least 20,000 refugees a year up to 2020. Many EU governments are reluctant to take in more refugees and are at odds over how to share out responsibility.
Almost 24,000 migrants have arrived on the coast of Italy this year, according to IOM figures. The largest numbers came from Gambia, Senegal, Somalia and Syria.
Last year there were some 170,100 arrivals, four times the 2013 total. They included more than 42,000 Syrians and 34,000 Eritreans, and nearly 10,000 Malians and 9,000 Nigerians.
Greece saw more than 12,600 arrivals by sea in the first three months of this year and 43,500 last year.
Thomson Reuters Foundation