Italy's president met political leaders on Tuesday before he was due to ask Romano Prodi to form a government to end more than a month of political limbo since the centre left narrowly won a national election.
President Giorgio Napolitano looked set to name Prodi prime minister later on Tuesday after consulting former presidents and party chiefs, including outgoing Prime Minister Silvio Berlusconi who said he still hoped to overturn his poll defeat.
Berlusconi said he told the head of state he had "noted the election result", but insisted parliament launch a probe into ballots from Italians abroad and those classed as void.
"As you know, there were many irregularities, many anomalies that we want cleared up," he told reporters after meeting Napolitano at the president's Quirinale palace.
By continuing to contest the election result, Berlusconi ruled out any idea of co-operating with the new administration, meaning Prodi will have to rely on the constant loyalty of his coalition to pass legislation and avoid government collapse.
Prodi's first spell in government ended prematurely in 1998 when the Communist Refoundation party deserted him in a confidence vote. The risk is there again, especially as he has just a two-seat majority in the upper house Senate.
Berlusconi, who ruled Italy for a record five years, scorned Prodi's bloc for installing leftist speakers in both houses of parliament and voting Napolitano, a former communist, head of state against the wishes of the opposition.
"This situation, resulting from the centre left's arrogant behaviour, is unprecedented and leads to a concentration of power never before seen in 60 years of the republic," Berlusconi said.
Prodi was still finalising his cabinet line-up after days of bickering between his coalition parties which range from the Christian Democrat centre to communists.