At least 45 migrants, including five children, have drowned in the deadliest shipwreck off Libya so far this year.
The UN’s agency for refugees says the deceased were among more than 80 people on board a vessel whose engine exploded off the coast of Zwara.
Local fishermen have rescued some 37 of the migrants.
The survivors, mainly from Senegal, Mali, Chad and Ghana, were detained after they disembarked in Libya
They have warned that without a rescue operation mechanism, more lives would be lost in the Mediterranean.
The UNHCR and the IOM have called Libya a risky destination to return migrants because o ongoing conflict, severe human rights violations, and arbitrary detention post-disembarkation.
More than 300 people are known to have died trying to cross the sea from Libya to Europe this year.