The International Organisation for Migration IOM said on Tuesday at least 50 people had died after a vessel carrying 75 Sudanese refugees caught fire off Libya's coast on Sunday.
The IOM said it had provided medical support to 24 survivors.
Libya has become a transit route for migrants fleeing conflict and poverty to Europe across the Mediterranean since the fall in 2011 of dictator Muammar Gaddafi during a Nato-backed uprising.