Leftist leader Pier Luigi Bersani said Monday that the government he has been asked to form would need to perform miracles to get recession-hit Italy back on track.
He was given the official go-ahead on Friday to try and form a government after February elections that left the country in political gridlock.
But he has come under increasing pressure from the centre right, led by rival Silvio Berlusconi, to share the task.
"The truth is that there is a dramatic situation... We need a government which performs miracles," Bersani said after consultations with trade unions ahead of talks with political parties on Tuesday.
The former Communist and head of the Democratic Party (PD) is seeking to establish a minority government reliant on votes from other parties in parliament.
He is set for talks with the centre-right on Tuesday and the anti-politics Five Star Movement on Wednesday, before meeting with President Giorgio Napolitano the next day to say whether he has been successful in garnering support.
"These are the crucial days for Bersani's attempt, but there's pessimism in the air. Instead of serious attempts to find an agreement, we have increasingly fiery controversies," said Stefano Folli, political expert for Italy's Il Sole 24 Ore newspaper.
The centre-left -- which won a majority in the lower house but not in the upper house in last month's vote, leaving it scrambling for support -- has so far ruled out allying with the centre-right led by Berlusconi.
Berlusconi's People of Freedom party (PDL) and allies came a close second in the election and are insisting that either Bersani accepts the idea of a "grand coalition" or the country holds a fresh vote.
"The election results showed two (political) forces which are essentially equal," said Berlusconi in a telephone interview on his own Canale 5 television station.
"It is wrong to waste time like this, because the economic situation in Italy is tragic. We need a solid government," said the the scandal-tainted three-time prime minister embroiled in a series of court cases.
The 76-year-old suggested Monday that his party would back Bersani at the head of a centre-left and right coalition if Berlusconi's second-in-command Angelo Alfano was made deputy prime minister.
But Bersani brushed off Berlusconi's offer of an alliance, saying: "Let's be serious. It's not possible to declare world war in the morning and then hug in the afternoon."
Any deal between Bersani and Berlusconi would anger supporters on the left and risk further dividing the PD.
Trade union leaders have called on Bersani to form a government "at all costs" and avoid a return to the polls which would slow down the implementation of key reforms they insist are needed to relieve pressure on ordinary citizens, from tax cuts to the reduction of political costs.
Meanwhile, Berlusconi appeared to be back on the campaign trail with fresh elections in mind, announcing more rallies across the country after tens of thousands of supporters flocked to hear him in Rome on Saturday.
Italy managed to pull back from its debt crisis under technocratic prime minister Mario Monti, who was brought in at the end of 2011 after Berlusconi was ousted by a parliamentary revolt amid European pressure and a wave of market panic.
But while Monti's austerity reforms and tax hikes reassured European leaders, the economy has failed to pick up and many Italians are suffering.
Official preliminary figures this month showed the country's unemployment rate shot up to 11.7 percent -- the highest level since at least 1992 -- while 38.7 percent of young people were without jobs.
Any new government will have to face the huge challenge of compromising between pressure at home to ease austerity, and European insistence on Italy sticking to its economic targets.