The possibility of Italy's anti-establishment 5-Star Movement and centre-left Democratic Party (PD) forming a coalition government looked doomed on Monday after senior figures from the two parties clashed.

Italian politics have been in limbo since an inconclusive vote on March 4, which saw a centre-right alliance led by the anti-immigrant League win the most seats and the 5-Star emerge as the biggest single party. The PD came a distant third.

After efforts by the right and 5-Star to join forces floundered, President Sergio Mattarella asked 5-Star chief Luigi Di Maio and the centre-left to discuss a possible deal.

The PD's leadership is due to meet on Thursday to decide whether to start coalition talks, but the party's outgoing head, former prime minister Matteo Renzi, said on Sunday he was against the idea, firmly reducing the chances of any pact.

"The Democratic Party lost, I resigned, seven out of 10 Italians voted for (League leader Matteo) Salvini or Di Maio. It's up to them to govern," he told RAI television.

"We can not sneak back in by the window after the Italian people have shown us the door," Renzi added.

Although he relinquished the reins of power within the PD after last month's stinging election defeat, Renzi still carries much sway within the party.

Soon after he spoke, Di Maio issued a short statement on Facebook, suggesting a deal with the PD was impossible.

"Today we have seen the proof that Renzi and his outsized ego still decide everything within (the PD)," Di Maio wrote. "We have done everything to put together a government in the interests of Italians. The PD said no ... and will pay for it."

He promised to make a fresh statement on Monday. "There will be news!" he wrote.