According to MANA, The four dead had suffocated, according to the Malta-based humanitarian group Migrant Offshore Aid Station (MOAS), whose Topaz Responder rescue ship recovered the bodies and 400 survivors from the same boat.
Italy has long been on the front line of seaborne migration from Africa to Europe, and is now the main point of entry after the European Union struck a deal with Turkey to stem flows to Greece.
Slightly fewer migrants arrived on Italian shores in the first six months of 2016 compared with the same period last year, but the number of deaths on the route has risen, according to the International Organisation for Migration (IOM).
The coast guard, said six rescue operations had rescued 945 people on Tuesday within about 30 miles (48 kilometers) of the Libyan coast.
All six boats, are believed to have set off from Libya, where criminal gangs have taken advantage of the breakdown of order to charge people hundreds or even thousands of dollars for the perilous crossing.
Italy's Navy said one of its helicopters had air-lifted one migrant suffering respiratory problems to the island of Lampedusa.
More than 67,000 seaborne migrants arrived in Italy between January 1 and July 3, according to the IOM.