Italy's supreme court has ruled that centre-left leader Romano Prodi won last week's general election, dismissing complaints by Prime Minister Silvio Berlusconi that the vote was marred by irregularities.
The ruling opens the way for Mr Prodi to start work on forming a new government which, because of constitutional complications, is not expected to take office before the end of May.
The Taoiseach has congratulated Mr Prodi on the victory of his coalition.
In a statement, Bertie Ahern said he had worked with Mr Prodi during his previous period as Italian Prime Minister and later when he presided over the European Commission.
Mr Ahern said he was writing to say how much he looked forward to working with Mr Prodi again.
Mr Berlusconi refused to concede defeat after the closest Italian election in modern history, saying he hoped checks on disputed ballots would show he won the vote.
At one point he said the election had been rigged, but later rowed back on his comments.
After a week of checks across Italy, the supreme court said in a statement that Mr Prodi won the election in the lower house by 24,755 votes. Provisional results last week said the winning margin was a slightly higher 25,224 votes.
Despite his tight victory, Mr Prodi's coalition will have almost 70 more seats than the centre-right in the 630-seat lower chamber, thanks to new rules introduced by Berlusconi last year. In the Senate, however, it will have a two-seat majority.
Under the Italian constitution, the head of state formally gives the election winner the mandate to govern.
But the transition process is complicated this year because President Carlo Azeglio Ciampi's term expires on May 18 and he wants his successor to nominate the new prime minister.
The new parliament, together with regional representatives, will pick a successor to Ciampi on 12-13 May.
