The Tunisian Red Crescent said 43 migrants drowned after their boat sank off Tunisia.
The migrants had set off from the Libyan port of Zuwara and were trying to cross the Mediterranean to reach Europe.
The head of the Tunisian Red Crescent, Mongi Selim, said the Tunisian navy had rescued 84 others.
Summer weather has seen an increase in the number of migrants trying to reach Europe from North Africa.
The Red Crescent said the boat that set sail on Monday night was carrying people from Egypt, Sudan, Eritrea and Bangladesh. The ship capsized after its engine failed.
The Tunisian Defense Ministry said those rescued off the Tunisian fishing port of Zarzis ranged between 3 and 40 years old.
Local radio reported that the Tunisian Red Crescent provided them with food and drink while searching for a place to shelter them during the required isolation period for the Covid virus.
Libya has been a major transit point for migrants from many countries trying to reach Europe via the Mediterranean.
But Tunisia has also become a major hub and has called on the European Union to deal with migration by helping to fight poverty in Africa.