Official returns released by the Interior Ministry showed Prodi's coalition had won a majority in both houses of parliament. The vote count -- which was extremely close -- must still be confirmed by Italy's highest court.
But Berlusconi disputed the results, alleging many irregularities in the vote count.
He also suggested the center-left and his own center-right bloc might work together to form a government of national unity.
Prodi dismissed Berlusconi suggestion of a left-right coalition.
His center-left bloc accused Berlusconi of seeking to subvert the election result.
(compiled from agency reports)