At least 45 migrants and refugees, including five children, have died in the deadliest shipwreck outside Libya this year, the UN refugee agency says.
They were among more than 80 people on board a ship whose engine exploded off the coast of Zwara, the UNHCR said.
The deaths were reported by some 37 survivors rescued by local fishermen.
Both the UNHCR and the International Organization for Migration (IOM) have called for search and rescue efforts for migrants.
They said that without a dedicated search and rescue mechanism, more lives would be lost in the Mediterranean.
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More than 300 people are known to have died this year and were trying to cross the sea from Libya to Europe, with the actual figure believed to be much higher.
Since the 2011 coup and assassination of its former leader, Muammar Gaddafi, Libya has become a major transit country for migrants.
But conditions for migrants there are dangerous, with the UNHCR and the IOM warning that they “were in danger of the ongoing conflict, serious human rights violations, and arbitrary detention post-disembarking”.
The survivors of Wednesday’s shipwreck, who were mainly from Senegal, Mali, Chad and Ghana, were detained after sinking in Libya.
There are reports of migrants being treated horribly in Libya, especially when they fall into the hands of soldiers and smugglers, who abuse them and try to extract money from them.