Matteo Salvini, whose anti-immigrant Northern League scooped the most votes among parties in the centre-right alliance that came out on top in Monday's national election, has ruled out a coalition government with the populist Five Star movement - now Italy's largest party.
"No to strange coalitions. No, no, no..." Salvini said.
The Northern League took 17.4 percent of ballots compared with 14 percent for ex-premier Silvio Berlusconi's conservative Forza Italia party. The centre-left Democratic Party got 18.7 percent of votes and Five Star 32.6 percent.
Although the centre-right alliance won 37 percent of Sunday's vote - far ahead of the centre-left alliance's 24 percent - it fell short of winning a ruling majority.
Voter turnout in Sunday's election was 72.93 percent, 2.3 percent lower than in 2013, according to Italy's interior ministry.
Northern League and Forza Italia had agreed before Sunday's polls that whichever party won more votes could choose the next prime minister, should their coalition come to power.
Italy's president Sergio Mattarella will by end-March invite a party leader to try and form a new government - a process that could take many more weeks of negotiation and coalition-building.
Though no party will be able to rule alone, 31-year-old Five Star leader Luigi di Maio and Salvini, 44, have both claimed the right to govern Italy.
The surge of support for populist, eurosceptic parties has been compared with Brexit and the election of Donald Trump in the United States.
