Two patrol boats "recovered nearly 500 people during six rescue operations, including one involving an inflatable boat which was only just about floating, and from which some migrants had fallen into the sea," it said in a statement.
"Six bodies were recovered so far. Search and rescue operations for survivors are continuing," added the navy, which has deployed significant resources off the Libyan coast.
A huge wave of migrants arrived in Italy at the end of August, when some 14,000 people were rescued in the space of five days.
Italy is sheltering growing numbers of would-be refugees as its neighbours to the north move to tighten their borders and make it harder for migrants to travel to their preferred destinations in northern Europe.
According to interior ministry figures this month, Italy now has 148,000 asylum seekers in reception centres, compared with 103,000 in 2015 and 66,000 in 2014.