Nascent coalition negotiations between Italy's far-right and anti-establishment political forces suffered a bump in the road on Monday when nationalist League leader Matteo Salvini said "key issues" remained unsolved and the Five Star Movement asked for more time to close a deal.

Following a weekend of intense negotiations, the leader of the anti-establishment Five Star Movement Luigi Di Maio and Matteo Salvini, leader of the far-right party League, had been widely expected to announce a "government agreement" and a nominee for prime minister on Monday afternoon.

But speaking to the press after a meeting with President Sergio Mattarella, Salvini seemed to cast doubt on the feasibility of an accord, saying that the two parties had "different visions" on certain "key issues" such as infrastructure, immigration and Italy's relations with the European Union. 

Local media suggested the pair had agreed step back from their political ambitions and nominate a neutral candidate for the premiership, but were struggling to agree on a nominee. Both leaders insisted on Monday that no names would be made public before they had been approved by Mattarella. A 71-year-old university professor, Giulio Sapelli, claimed on Monday he had spoken to both leaders and was willing to do the job, but a Five Star source told Reuters he was not the party's top pick.

Salvini insisted that his party wanted a "free hand" to deal with illegal immigration and reiterated his euroskeptic stance, demanding the right to re-negotiate the EU's tight fiscal rules.

"If I go to the government, I want to do what I promised the Italians," he said, adding that his party was not afraid to return to the polls if discussions failed.

Earlier in the afternoon Di Maio had adopted a more optimistic tone, telling reporters he had asked Mattarella for "a few more days" to come to an agreement with the League. He added that a finalized deal would be put to an online vote for Five Star members.

Italy has been in political deadlock since an inconclusive March 4 election, which was dominated by concerns over a struggling economy, the refugee crisis and illegal immigration. 

Five Star and the League have been negotiating a power-sharing deal since last Wednesday, when Salvini's right-wing coalition partner, former prime minister Silvio Berlusconi, gave the green light for the pair to form a government without his Forza Italia party.

But reaching a deal is likely to be a challenge given the parties' vastly different stances on a wide range of issues. Salvini and Di Maio had reportedly been willing to make compromises over their flagship policies -- the League's drastic drop in taxes and Five Star's universal basic income -- which look tricky to reconcile in one of the eurozone's most indebted countries.

At the March polls, Five Star emerged as Italy's largest single party in parliament by far after winning nearly 33 percent of the vote. Salvini's League won 17 percent of votes, but it was part of a right-wing alliance including Berlusconi's Forza Italia that garnered 37 percent of the vote. 

On Monday, Salvini claimed to be speaking on behalf on the 12 million people who voted for the right-wing coalition in March, despite entering into negotiations with Five Star Movement without his allies, and Berlusconi saying his party would not back a Five Star-League alliance in parliament.

(With input from agencies)