The prime minister also observed a minute's silence in honour of the victims, before addressing a conference in Athens on Monday.
Thirty-eight people were killed and at least a dozen injured when a bus careered off a road close to Naples and fell 30 metres down a slope on Sunday night.
The reason for the crash is as yet unknown, although investigators are looking into possible manslaughter. The bus, carrying around 50 people, had been travelling at high speed when it crashed.
Passengers were returning from a pilgrimage to Pietrelcina, the birthplace of Saint Pio, an Italian priest canonised in 2002 who is highly venerated in southern Italy.