Nearly 1,000 refugees were saved in six separate rescue operations in the Mediterranean on Tuesday, while four were found dead below the deck of their boat, Italy's coast guard said.
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 amid Europe's worst refugee crisis since World War Two.
The Greek coastguard said on Wednesday that four refugees also drowned and six were rescued when a small boat laden with migrants overturned off the Greek island of Lesbos. The victims included two children.
Slightly fewer refugees arrived on Italian and Greek shores recently compared with the same period last year. But according to the International Organisation for Migration (IOM) the number of deaths on the route to Italy has risen.
The coast guard, whom rescuers have to contact when they pick people up at sea, said six rescue operations had rescued 945 people on Tuesday within about 30 miles (48 km) of the Libyan coast.
All six boats, including four rubber dinghies, 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.
As well as MOAS, fellow humanitarian agencies Doctors Without Borders, Germany-based Sea-Watch, and the EU rescue ship Reina Sofia took part in the operations, which were coordinated by the coast guard in Rome.
Italy's Navy said one of its helicopters had air-lifted one refugee suffering respiratory problems to the island of Lampedusa and that two of its own ships had been involved in rescues.
Emergency, a medical humanitarian organisation, also treated one person who was found on the wooden boat in a critical condition, MOAS said. It was not clear if this was the same person air-lifted to Lampedusa.
More than 67,000 seaborne refugee arrived in Italy between Jan. 1 and July 3, according to the IOM.