The populist 5-Star Movement (M5S) on Monday pulled out of an alliance with the centre-left Democratic Party (PD) to run together at next month's regional elections in Sicily.
The decision reflects the breakdown of the alliance at a national level for the September 25 general election.
The PD exited the latter alliance after the M5S started a party rebellion that resulted in the resignation of outgoing Premier Mario Draghi.
M5S leader and former premier Giuseppe Conte announced the Sicily split on Facebook saying "in Sicily the 5-Star Movement will run alone, to give redemption and dignity yo all the island." He reportedly told supporters "going it alone in Sicily we'll get more votes," holding up an opinion poll.
Conte said that despite the PD "choosing the Draghi agenda and reneging on everything progressive achieved" under Conte's premiership, he had tried to keep up the Sicily alliance but the PD had not "given adequate answers".
PD leader and former premier Enrico Letta had previously pulled out of their budding alliance with the M5S after the M5S was the prime mover behind a rebellion that forced Draghi to resign and trigger snap elections last month.
The M5S, which has bled support since winning a third of the vote at the 2018 general election, is now polling at around 11% and will run alone.
Matteo Salvini's nationalist League party and three-time ex-premier and media magnate Silvio Berlusconi's centre-right Forza Italia (FI) party swiftly jumped onto an anti-Draghi bandwagon after the M5S started the ball rolling by boycotting an aid package because it would have given Rome a waste to heat plant, an anathema for the green-leaning party.
Conte had previously voiced unease on several occasions with Draghi, who replaced him as premier in early 2021.