Opposition leader Silvio Berlusconi threatened Monday to withdraw his coalition from Parliament if it turns out that his side won general elections in April and the president refuses to call a new vote, according to news reports. Berlusconi's conservative coalition narrowly lost last month's election to the center-left coalition of Romano Prodi. The April 9-10 vote was so close that the final results were not certified for days as localities counted contested votes, and the narrow margin highlighted a bitterly and virtually evenly divided nation. Prodi eventually was sworn in last week after receiving the mandate from the country's new president, former Communist Giorgio Napolitano. But Berlusconi has repeatedly challenged the results. He vowed Monday during the taping of the late-night TV talk show "Porta a Porta" that if a check of the vote shows that he won rather than Prodi, and Napolitano did not call for new elections, he would order "the immediate withdrawal of all the deputies and senators of the House of Liberties coalition," according to the show's transcripts cited by the Apcom and ANSA agencies. Berlusconi did not say whether he had officially appealed the election results. According to Italian law, all complaints regarding blank, null or otherwise irregular ballots must be taken up by legislative commissions formed once the new parliament convenes.