The United Nations refugee agency says it has received witness accounts that a ship carrying about 600 refugees trying to reach Europe sank and broke up off the Libyan coast, and many of those on board died.
The agency said 16 bodies, including two babies, had been found, the BBC reports.
It says the ship broke apart on Friday, not far from the shore, and witness accounts are only now emerging.
One Somali woman said she swam to safety but her four-month-old baby drowned.
The Italian coastguard which carries out patrols of the Mediterranean said it had no knowledge of the accident.
UNCHR has said all ships using the Mediterranean should be ready to assist such vessels, as thousands continue to flee North Africa in inadequate boats.
In a separate incident, NATO has denied claims that its naval units left dozens of migrants to die aboard another boat in distress.
The Guardian newspaper said 61 of the 72 people on board died of thirst and hunger despite the boat making contact with a military helicopter and warship.
However NATO said it was unaware of the plight of the boat, which reportedly was adrift for more than two weeks.