At least 400 migrants are believed to have been drowned as their boat capsized off Libya, survivors said.
They said that the boat, which was carrying about 550 migrants, overturned a day after leaving Libya, reported the BBC.
The Italian coast guard rescued about 144 people on Monday and launched air and sea operation to find the remaining migrants.
About nine bodies have been recovered so far but no more survivors have been found since then.
More than 7,000 migrants have been rescued from the Mediterranean since Friday, the European Union said.
Migrants have been pouring in as the migration season has just started.
The EU last year reduced its maritime rescue operations in a bid to discourage more migrants from moving to the region. However, latest figures showed that the policy failed to deter people.
