A left-leaning faction in Italy's Democratic Party, led by its former leader Pier Luigi Bersani and ex- lower house of parliament whip Roberto Speranza said on Tuesday they were breaking away from the ruling centre-left group.
The rebels said they would take no part in further meetings or the party congress later this year but would continue to back caretaker Italian premier Paolo Gentiloni, who is close to reformist ex-premier Matteo Renzi.
Another Renzi critic, Michele Emiliano, governor of Italy's southern Puglia region announced on Tuesday that he would remain in the Democratic Party and would run in upcoming leadership primaries.
The small but influential splinter group could get between 5 percent and 8 percent of votes in a future general election, according to pollsters.
Bersani, Speranza and other leftwingers including Tuscany regional governor Enrico Rossi have long criticised Renzi's repositioning of the party towards the political centre and his allegedly autocratic treatment of dissenters.
Renzi effectively triggered the split when he quit as Democratic Party leader on Sunday to seek a new, stronger mandate in early primaries, while urging unity, a call echoed by party founders including ex-premier Romano Prodi.
Prodi warned it would be political "suicide" for leftwingers to break away at a time when populist forces like the grassroots Five Star movement and the anti-immigrant Northern League party were poised to make headway in the next polls.
Renzi stood down as prime minister in December after a crushing defeat in a referendum on constitutional reforms he claimed would streamline Italy's political machinery. The planned reforms included scrapping the upper house of parliament as a directly elected body.
The former premier is eager to return to power and is pushing for national elections to be held this year rather than early 2018 as scheduled.
