At least 20 refugees dead after 4,000 rescued in single day

Migrants wait to disembark from the Italian Navy ship Bettica as it arrives at the Sicilian Porto Empedocle harbour (AP)

At least 20 refugees have died trying to reach Europe after their boat sank off the coast of Libya.

The death toll is likely to grow far higher, however, as the Libyan coast guard also reported two overturned boats between the coastal cities of Sabratha and Zwara. Only four bodies were found, raising fears that the rest of those on board had died.