Italian prosecutors blamed the captain of a grossly overloaded fishing boat for a collision that capsized and sank his vessel off Libya, drowning hundreds of migrants including many women and children locked below deck.

The few survivors of Sunday's tragedy told investigators how the African and Bangladeshi migrants, among hundreds of thousands trying to escape war and poverty, had waited up to a month in Libya before the boat set sail for Europe. One said he had suffered a beating at the hands of people traffickers.

The heavy loss of life among the migrants, who paid hundreds of dollars in the hope of getting over the Mediterranean, has put heavy pressure on European leaders to respond effectively to a dramatic rise in deaths among people attempting the crossing.