Berlusconi fury as Monti throws down gauntlet in election fight
He also vowed to launch a parliamentary inquiry into the 2011 fall of his government and the appointment of Mr Monti as president.
Mr Berlusconi lashed out after Mr Monti ended weeks of speculation and announced he would head a coalition of centrist forces, businessmen and pro-Vatican forces in the February 24-25 elections.
But Mr Berlusconi said he never expected Mr Monti would renege on his repeated assurances that he "wouldn't use the public prominence as head of a technical government for an ulterior presence in politics".
He said the decision represented a "loss of credibility" for Mr Monti, a respected economist and former European Commissioner, and said if he is elected premier he would launch a parliamentary inquiry into the fall of his government.
"There was a serious wound to democracy inflicted not just on us but on all Italians," Mr Berlusconi said as he arrived in Milan from Rome.
Mr Berlusconi's People of Freedom party, beset by local corruption scandals and still tainted by Mr Berlusconi's last term, trails the centre-left Democratic Party in the polls.
The Democrats, headed by Pier Luigi Bersani, are expected to win the election with about 30pc of the vote.
Mr Monti was named by Italy's president to lead a technical government after Mr Berlusconi, hobbled by sex scandals, legal woes and defections, was forced to resign in November 2011 amid Italy's slide into the eurozone's debt crisis.
Mr Berlusconi's party, the parliament's largest, had initially supported Mr Monti, backing tax hikes, raises in the retirement age and other reforms deemed necessary to restore financial credibility.
But earlier this month, Mr Berlusconi yanked his party's support, accusing Mr Monti's government of leading Italy into a "spiral of recession".
Mr Monti promptly resigned, forcing elections to be moved up by about two months.