IOM said the bodies of six migrants had been removed while 29 others were missing and presumed dead. It is not immediately clear what caused the wooden boat to capsize.
The tragedy was the latest to involve migrants leaving North Africa to seek a better life in Europe. In the past week alone, at least 53 migrants have been reported dead or presumed dead off the coast of Libya, according to IOM.
Earlier this month, more than 90 people in an overcrowded boat drowned in the Mediterranean Sea, days after leaving Libya, according to aid group Doctors Without Borders.
Migrants regularly try to cross the Mediterranean from Libya in a desperate attempt to reach European shores. The country has become the main transit point for migrants fleeing war and poverty in Africa and the Middle East.
In recent years, human traffickers have taken advantage of the chaos in Libya, smuggling migrants across the long borders of the oil-rich country with six nations. Migrants are then usually crammed into ill-equipped dinghies and set off on risky sea voyages.
At least 476 migrants died along the central Mediterranean route between January 1 and April 11, according to IOM.
Once back in Libya, migrants are usually taken to government-run detention centers where abuse and mistreatment prevail.
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