Moments earlier, a 5-Star source had said the programme had been substantially agreed and that it contained no reference to a possible exit from the euro or "anything that could cause any concern regarding Italy's euro membership".
Italy's two anti-establishment parties have signed an accord to form a ruling coalition, promising to ramp up spending and putting the nation on a collision course with the EU, Reuters reported.
As Italy moves closer to the formation of a government between the anti-establishment 5-Star Movement (M5S) and Lega (League), a leak to Huffington Post of a 40-page policy contract between the two Eurosceptic parties that details their roadmap rattled global markets on Wednesday.
Luigi Di Maio, the leader of M5S, emerged from a meeting with the League's counterpart Matteo Salvini saying a pact could be sealed by Thursday evening.
Chances for a League-5-Star government got a boost last week after Berlusconi said he wouldn't get in the way of it, but wouldn't vote for it either.
Both parties have a history of Euroscepticism. 5-Star has moderated its position considerably in the a year ago, rowing back on a previous plan to hold a referendum on Italy's membership of the currency bloc.
Attention will now shift to their party votes, with Di Maio promising that Five Star members will have an online vote, while the League plans to set up ballots in piazzas across the country.
Both leaders said the final policy document would be put to their voters before being submitted to the president, Sergio Mattarella, who has the final say on the contract, prime minister and cabinet lineup. Di Maio, 31, said earlier this week that tax evaders would be jailed.
Italian markets jolted by 5-Star, League coalition proposals
A draft of the accord reviewed by Reuters earlier on Thursday spelt out a spending plan that would breach European Union rules on fiscal discipline: cutting taxes, increasing welfare payments for the poor and scrapping an unpopular pension reform.
The policies would cost many billions of euros and have spooked investors in Italian debt, shares and the euro.
Plans by Italy's rightwing League party and the populist Five Star Movement to "rethink" European Union (EU) fiscal constraints and oppose worldwide trade treaties drove Italy's borrowing costs up Thursday.
The gap over benchmark German Bund yields widened to 148 bps, its widest since the day after Italy's March 4 election.
The likely arrival of a populist government took its toll on the Italian banking sector at the Milan Stock Exchange Thursday, in particular the Monte dei Paschi di Siena bank, majority-owned by the Italian state, which saw its share price tumble.
Claudio Borghi said Monte Paschi will remain in public hands following a bailout past year and branch closures planned by the outgoing centre-left government would be rolled back.
Outgoing Italian Prime Minister Paolo Gentiloni told a meeting of European Union leaders in Bulgaria that he and other leaders were anxious that fundamental issues such as the need to safeguard public accounts were now up for political discussion.
Mattarella has repeatedly stressed the importance of maintaining a strong, pro-European stance. The contract for the M5S-League government features plans to introduce a two-tier flat tax, a basic income and the revision of a 2011 pension reform that raised the retirement age, among other measures.