Final results from the Italian general election show that the centre-left coalition of former the European Commission President, Romano Prodi, has won with a slender majority in both houses of parliament.
However the outgoing Prime Minister, Silvio Berlusconi, has claimed there were many irregularities in overseas voting and said he would not concede defeat without a recheck.
Mr Berlusconi raised the prospect of declaring invalid the pivotal votes for six Senate seats chosen by Italians living abroad.
That vote swung the election to Mr Prodi with four of the six seats going to the centre-left alliance, leaving them with 158 seats compared to 156 for Berlusconi's grouping.
A full count had already shown Romano Prodi as the winner in the lower house with a slight majority of just 25,224 votes.
Under Italy's new electoral system, the ballot winners are automatically granted 340 of the lower house's 630 seats no matter how small their margin of victory in the popular vote
However, each chamber in the Italian parliament has equal power, meaning both houses must be secured for a government to rule effectively. The disputed result, given the small margin of victory, has raised fears political paralysis in Italy.
A proposal by Mr Berlusconi to create a 'grand coalition', similar to that in Germany, has been rejected by the centre-left alliance which has accused the 69-year-old incumbent of seeking to subvert the election result.
The close race has revealed deep splits in Italian politics and raised the spectre of chronic instability in the months ahead.