Up to 700 migrants are feared drowned in a series of shipwrecks off the coast of Libya in the last few days, the UN refugee agency says.
The boats sank south of Italy on Wednesday, Thursday and Friday as the migrants tried to reach Europe in unseaworthy vessels.
Spring weather has led to a surge of people attempting the perilous crossing from Africa to Europe.
Almost 100 migrants are missing from a smugglers' boat which capsized on Wednesday. Horrifying pictures of the incident and its aftermath were filmed by rescuers.About 550 other migrants are missing from a boat which overturned on Thursday morning after leaving the Libyan port of Sabratha on Wednesday. Survivors said the boat had no engine and was being towed by a second smuggling vessel.
In a third shipwreck on Friday, 135 people were rescued, 45 bodies pulled from the water and an unspecified number of others are missing.
Meanwhile, the MSF Sea group suggested the death toll from the last week could be as high as 900.
Survivors are being taken to the Italian ports of Taranto and Pozzallo.