At least 40 people are feared dead after another boat capsized off the coast of Libya on Tuesday, according to the United Nations refugee agency (UNHCR).
"Terrible news coming in of potentially large loss of life in a shipwreck off the coast of Libya," Charlie Yaxley, a spokesman for the UNHCR, said on Twitter.
"Around 60 people have been rescued and returned to shore. At least 40 people are estimated to be dead or missing," he added.
Alarm Phone, an independent support group for people crossing the Mediterranean Sea, said up to 100 people were onboard the capsized vessel, Al Jazeera reported.
The group added that it received a call from those on the boat, who "were in severe distress, crying and shouting, telling us that people had died already".
"These tragedies are preventable. Cannot accept large loss of life each month as normal," Yaxley wrote on Twitter, calling for the return of European Union vessels in rescue efforts and for NGOs to be "free to save lives at sea".
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Across the Mediterranean, more than 850 deaths have so far been recorded this year.
After the NATO-backed uprising that toppled and killed longtime ruler Moammar Gadhafi in 2011, Libya became a major conduit for African migrants and refugees seeking a better life in Europe. Traffickers and armed groups have exploited Libya's chaos since his overthrow, and have been implicated in widespread abuses of migrants, including torture and abduction for ransom.
In recent years, the European Union has also partnered with Libyan coastguards and the country's forces to prevent people from making the sea journey to Europe.