The Italian navy has found the bodies of 30 migrants crammed into the hold of an overcrowded smugglers' boat, which was trying to reach Italy's southern coast.
The corpses were discovered in the bow area of the vessel which was carrying a further 556 people, the navy said.
Medical personnel said that, according to a preliminary assessment, the victims died of asphyxiation or drowning during the crossing.
A navy spokeswoman told IBTimes UK that it was not immediately clear whether the migrants were dumped into the hold after they died, or if they suffocated there because they were packed in too tightly.
It wasn't clear whether the boat was taking on water when it was intercepted. An investigation has been launched, the navy said.
At the time of writing the boat was being towed to the southern Sicilian port of Pozzallo by the navy frigate Grecale, which took the survivors on board.
In total, more than 5,000 migrants were rescued over the weekend by the navy, adding to the 60,000 who have reached Italy, mainly from northern Africa, since the beginning of the year.
The growing number of arrivals is on track to exceed the yearly record of 62,000 set in 2011 during the Arab Spring uprisings and local communities are struggling to cope.
The mayor of Pozzallo, a seaside town of 19,000 people on the southern tip of Sicily, said the local mortuary has no room for 30 more bodies.
"The only two spaces we have in the cemetery's cold room are already hosting the bodies of another two migrants," said Mayor Luigi Ammatuna.
Italy beefed up its sea rescue operations last October after hundreds died as a migrant boat capsized.
More than 900 navy personnel, five vessels and several aircraft have been deployed as part of the so called Mare Nostrum (Our Sea) operation, which the navy says has saved more than 20,000 lives since its launch.
However critics of the operation, which costs €9m a month, claim that it eases the human traffickers' job and encourages further immigration.
Matteo Salvini, leader of the xenophobic Northern League Party, said that Prime Minister Matteo Renzi and Interior Minister Angelino Alfano have "their shirts dirty with blood."
The government has accused the European Union of leaving Italy alone in addressing the migration problem, and said it will use its EU presidency, which begins this week, to press its case.