Around 40 people are feared to have drowned after falling out of a rubber boat in the latest tragedy in the Mediterranean.
The inflatable, carrying more than 100 migrants, sank between Libya and the Italian island of Sicily on Sunday, according to survivors.
The tragedy happened when a commercial vessel approached to rescue the boat, it was reported.
According to the charity Save The Children, survivors who have now arrived in Catania, Sicily, said the inflatable boat deflated or exploded.
Then dozens of their fellow passengers fell into the water, could not swim and drowned.
Save the Children's Giovanna di Benedetto said some survivors claimed "very many" died, while others put the number of dead at "around 40".
Over three days from last Friday to Sunday, the Italian coastguardrescued several thousand migrants in the Mediterranean.
It came after smugglers in Libya took advantage of calm seas and warm weather to send many of them out into the sea in overloaded rubber boats and fishing vessels.
Last month, up to 900 migrants drowned when their boat capsized off Libya with hundreds of passengers thought to have been locked in the hold by smugglers.
A few days earlier, a further 400 people were feared drowned in another capsizing.
After the deaths, the European Union held an emergency summit and agreed to contribute more boats and patrol aircraft to Mediterranean rescue efforts.
EU chiefs also want to push for a UN resolution that would allow them to destroy vessels used by traffickers before they attempt to smuggle migrants across the water.
More than 1,750 people are estimated to have died in the waters between Libya and Italy since the start of this year.