The boat had set off from Zuwarah on Libya’s northwest coast, carrying migrants and refugees from Egypt, Sudan, Eritrea and Bangladesh, as they tried to cross the Mediterranean to Italy, the organisation said.
“The Navy rescued 84 migrants and 43 others drowned in a boat that set off from Libya’s Zuwara towards Europe,” Red Crescent official Mongi Slim said.
Libya is a frequent departure point for Europe-bound migrants making the dangerous Mediterranean Sea crossing.
Since 2014, more than 20,000 migrants and refugees have died at sea while trying to reach Europe from Africa.
At least 866 people are feared to have drowned while making the journey across the Mediterranean from North Africa this year.
More than 40 people died when a boat sank off Tunisia’s coast in April. In March, 39 died off the coast of Sfax.
In June last year, at least 60 were killed when a boat sank.