Italy's largest opposition party, the Democratic Party, has presented a roster of candidates for the European Parliament elections next month that includes a Lampedusa doctor who has treated migrants saved at sea over many years and a prominent anti-mafia prosecutor.

Party leader Nicola Zingaretti acknowledged during a news conference in Rome on Friday that the elections "will be a difficult battle," but that the party would confront them with "great conviction."

The center-left party was once a powerful force in Italian politics, and most recently won a 2013 election. But it suffered a heavy defeat in a national election last year to the populist 5-Star Movement and the anti-migrant League, who now govern in a coalition.

The Democratic Party's candidates include the doctor, Pietro Bartolo, and anti-mafia prosecutor Franco Roberti.