At least 74 migrants drowned after their Europe-bound ship broke down off the coast of Libya on Thursday, the UN migration agency said.
The incident is latest of at least eight shipwrecks in the Central Mediterranean since last month.
The boat was carrying more than 120 migrants, including women and children, when it capsized off the coast of the Libyan port of Al Khums, said the International Organisation for Migration.
Only 47 people were rescued by the Libyan coastguard and fishermen and brought to shore.
So far, 31 bodies have been retrieved as the search for the remaining victims continues, the IOM said.
In the years since the 2011 uprising that ousted and killed longtime dictator Muammar Qaddafi, war-torn Libya has emerged as the dominant transit point for migrants hoping to get to Europe from Africa and the Middle East.
Smugglers often pack desperate families into ill-equipped rubber boats that stall and flounder on the perilous Central Mediterranean route. At least 20,000 people have died in those waters since 2014, according to the IOM.
"The mounting loss of life in the Mediterranean is a manifestation of the inability of states to take decisive action to redeploy much needed, dedicated search-and-rescue capacity in the deadliest sea-crossing in the world," said Federico Soda, IOM Libya chief of mission.
Six people died after a Europe-bound rubber boat carrying 116 migrants and asylum-seekers fell apart in the Central Mediterranean, a Spanish humanitarian group said on Wednesday.
Rescuers pulled out 111 people alive, including two infants, and recovered five bodies. But one of the two infants, a six-month-old girl, died after being brought on board the rescue ship, Open Arms tweeted on their official account.
A day earlier, 13 African migrants, including three women and a child, drowned in a similar shipwreck off the Libyan coast.
The IOM said that it had noticed a recent surge in the number of departures from Libyan shores, with more than 780 arrivals in Italy since the beginning of October.
More than 11,000 migrants were intercepted and returned to Libya, where they face the risk of human rights offences and detention, the IOM said.
“IOM maintains that Libya is not a safe port for return and reiterates its call on the international community and the European Union to take urgent and concrete action to end the cycle of return and exploitation,” it said.
