The tragedy is the latest in a series involving people trying to make the short but perilous crossing from North Africa to Europe.
More than 300 migrants are feared drowned after their overcrowded dinghies sank in the Mediterranean on the way to Europe.
The victims are among migrants mainly from sub-Saharan Africa who had left Libya at the weekend in four small boats, the UN refugee agency said.
"This is a tragedy on an enormous scale and a stark reminder that more lives could be lost if those seeking safety are left at the mercy of the sea,"
Details emerged after nine survivors out of a group of more than 200 packed into two dinghies were rescued by the Italian coastguard and taken to the island of Lampedusa.
The International Organisation for Migration (IOM) said the surviving migrants from the latest disaster spoke French, so probably came from west Africa.
Its spokesman in Geneva Joel Millman told AFP that information was coming in about another stricken boat and warned that the overall toll may reach as many as 350.