ROME (AP) — The bodies of some 30 would-be migrants were found in in the hold of a packed smugglers’ boat making its way to Italy, the Italian navy said Monday.

The boat was carrying nearly 600 people, and the remaining 566 survivors were rescued by the navy frigate Grecale and were headed to the port at Pozzallo, on the southern tip of Sicily.

A navy statement Monday said that during the rescue operation, the 30 corpses were discovered in the bow area of the boat. The victims were believed to have suffocated or drowned during the crossing. Initial news reports said the migrants had suffocated because they were packed in so tightly. It wasn’t clear if the boat was taking on water when it was rescued.

Overall during the weekend, the navy said it rescued more than 5,000 migrants, adding to the 60,000 people who have made their way to Italy since the beginning of the year, compared with 42,000 in all of 2013.

Most are African or Middle Eastern refugees who pay hundreds or thousands of euros apiece to smugglers in Libya who pack them into unsafe fishing vessels for the crossing. Officials say the numbers have swelled this year due to the increasing instability in Libya.

Italy beefed up its sea rescue operations last October after a migrant boat capsized off the Sicilian island of Lampedusa, killing more than 360 people. Italy has insisted that the European Union shoulder more of the cost and burden of the rescue operations and says it will use its EU presidency starting Tuesday to press its case.