An Italian coast guard vessel brought the 17 corpses ashore at the port of Augusta on the southern island of Sicily on Sunday, after they were discovered on a rubber dinghy in the Mediterranean, Deutsche Welle reported Monday.

Italian prosecutors have launched an investigation into how they died. The Italian vessel also arrived with more than 450 survivors on board.

Frontex said in a statement posted on its website that its operation Triton, which is meant to prevent loss of life in the Mediterranean, had rescued more than 5,000 people since Friday.

It said the rescue operations since then, migrants who left the coast of Libya in 25 boats had been picked up by 22 ships from Italy, Britain, Malt and Belgium, which were assisted by spotter planes from Iceland and Finland. It said that more than 4,200 migrants had been picked up in that effort on Friday alone.

It also said German, Irish and Danish vessels were involved in the weekend's operations.

"This is the biggest wave of migrants we have seen in 2015," Frontex Executive Director Fabrice Leggeri said.