Italian centre-left leader Romano Prodi held firm to his disputed election victory Wednesday despite Prime Minister Silvio Berlusconi's refusal to step aside due to allegations of "irregularities".

Centre-left Union leader Romano Prodi celebrates at the union's headquarters in Rome. Prodi held firm to his disputed election victory despite Prime Minister Silvio Berlusconi's refusal to step aside due to allegations of "irregularities". [AFP]

"We cannot recognise the outcome of a vote until there is a definitive clear judgement. Until that day, no one can say they have won," the billionaire prime minister told a packed news conference in Rome on Tuesday.

Berlusconi raised the prospect of declaring invalid the pivotal votes for six seats chosen by Italians living abroad. That vote had swung the election to Prodi's centre-left alliance, with four of the six seats going their way.

"On the foreign vote there were a great many irregularities," he said.

"It cannot be excluded that this vote can be declared invalid," said Berlusconi, who fought a vitriolic campaign to extend his five-year reign -- the longest since World War II.

He even offered the image of a German-style "grand coalition" in case a recount eventually ended with each side taking one house -- a divided parliament.

"I think maybe we should follow the example of some other European countries, like Germany, to see if there is a case for joining forces and governing together," he said.

Each chamber in the Italian parliament has equal power, meaning both the lower house Chamber of Deputies and upper house Senate must be secured for a government to rule effectively.

But Prodi quashed the idea of setting up government with Berlusconi's camp.

"We came into this election with a set coalition, and the electoral law has alloted us a number of seats in the Chamber (of Deputies) and in the Senate which will allow us to govern," he told journalists Tuesday outside his campaign headquarters in Rome.

Still, Berlusconi's declarations raised the spectre of a Florida-style recount debacle akin to the situation that brought his close ally US President George W. Bush to power in 2000.

Only minutes earlier, full results showed Prodi's Union alliance had snatched the elections from the conservative House of Freedoms coalition, after a campaign that had attacked the prime minister relentlessly over Italy's weak economy.

Prodi's centre-left bloc took control of the Senate, which had been hanging in the balance, the interior ministry said. A full count had already shown him as the winner in the lower chamber.

"Whoever wins, wins, that's the beauty of democracy," the sober 66-year-old economist, nicknamed "Il Professore", said earlier in the day.

But Berlusconi's own Forza Italia party had said it would press for a recount given the wafer-thin margin -- just 25,224 votes -- which separated the two sides in the lower house.

"There is a difference of 25,000 votes and there are 43,000 contested votes," Forza Italia's national coordinator Sandro Bondi said in a debate on Sky Italia television.

"For the moment, you have won nowhere: neither in the House, nor in the Senate," said Bondi.

The full results showed Prodi's team winning 158 seats of 315 seats up for grabs in the Senate, compared to 156 for Berlusconi.

The Prodi alliance also won 342 seats in the 630-seat lower house Chamber of Deputies compared to 281 for Berlusconi.

Among the first congratulations for the former European Commission president's election victory came from the current head of the European Union's executive, Jose Manuel Barroso.

Prodi had "actively promoted the general European interest" as commission chief and would "continue to work in this direction" as Italian premier, Barroso said in a statement, while also noting the "constructive and fruitful relationship" he had had with Berlusconi.

Outside Prodi's Rome headquarters supporters milled restlessly, awaiting a final, iron-clad confirmation he had won.

Gianni Marchetti, a 54-year-old biologist in Rome on holiday from northern Padua, said he hoped a "new Florida" could be avoided.

"It should have been such an easy victory," Marchetti said, ticking off Berlusconi's "notorious gaffes, his negative image overseas, his disastrous economic policies, the impoverishment of the people, Italy's decline on the world market..."

In the nearby Via del Corso, one of Rome's busiest shopping streets, Daniele Calicchia said he would not welcome a recount. "Berlusconi does his best to turn things his way. But that would not be good for Italy," said Calicchia, a volunteer raising money for a drug abuse program.

At a nearby clothing boutique, a saleswoman, Giusappina Vista, said she would not oppose a recount. "If there's a doubt, why not?"