The US has recognised the victory of the centre-left coalition in Italy's disputed elections.
The State Department said it looks forward to working with Mr Prodi
The Department of State said it looked forward to working with the bloc's leader, Romano Prodi, who was declared the winner by Italy's highest court.
Outgoing Prime Minister Silvio Berlusconi is still refusing to concede, calling for more checks.
Leaders from Britain, France and Germany had already called Mr Prodi to congratulate him.
US President George W Bush - a close ally of Italy's centre-right prime minister - last week held back from congratulating Mr Prodi, saying the election was being contested.
In its statement on Thursday, the State Department said there would be an "official conveyance" of congratulations from President Bush to Mr Prodi.
"We look forward to working with Mr Prodi's government and we look forward to working with Mr Prodi," said State Department spokesman Sean McCormack.
Mr Berlusconi is refusing to concede defeat
Mr Prodi has said there is no further doubts about his victory, and is working on forming a new government.
After a review of ballots, Italy's top court declared on Wednesday that his coalition had won the lower house of parliament by 24,755 votes.
Mr Berlusconi has not made any public comments since the court announcement.
His economy minister, Giulio Tremonti, told Italian TV that some "anomalies" were yet to be cleared up.
The national co-ordinator of Forza Italia, Sandro Bondi, said the court should widen its review to include "irregularities" in overseas voting.
However one of the parties in the centre-right coalition, the UDC party, has broken ranks and admitted defeat.