The United Nations refugee agency say 800 migrants died when a boat capsized in the Mediterranean at the weekend after speaking to survivors.

The captain and a crew member have been arrested and charged with people trafficking. The captain also faces a charge of reckless multiple homicide in relation to the disaster off the coast on Libya.

As the search continues for victims of the weekend disaster, coast guard ships rushed to respond to two new distress calls.

The calls were made from an inflatable life raft with 100 to 150 migrants on board and a boat carrying about 300 people, said Italy's Prime Minister Matteo Renzi.

Hours later it remained unclear how the Mediterranean rescue operations were going.

The International Organisation for Migration (IOM) said one of the callers reported that 20 people had been killed as the boat sank in international waters.

In a separate incident, at least three people, including a child, were killed when a boat carrying migrants ran aground off the coast of the Greek island of Rhodes.

At an already scheduled meeting in Luxembourg, they unveiled a 10-point plan which also involves doubling the size and funding of Triton, the Europe-wide border protection operation.

There has been a surge in migrants trying to reach European shores - usually Italy and Malta - as people flee conflict, repression and poverty in the Middle East and Africa.

At least 1,500 are believed to have drowned in the Mediterranean this year alone.

Yesterday, EU ministers announced measures to help stop the crisis in the Mediterranean - including a proposal to double the size of its search and rescue operations.

UN secretary general Ban Ki-moon says it's urgent that the EU cracks down on trafficking in the Mediterranean: