Berlusconi explained to members of his People of Freedom party, which has reverted to its old name of Forza Italia (Go Italy), the reasons why on Saturday he withdrew his support for the cabinet.
"I took the decision on my own in the night because Italians could not understand why we were in government with the left," the 77-year-old was quoted as saying at a party meeting.
"We have to remain united. We wash our dirty linen at home," he was quoted by participants as saying. "We have to explain our reasons to our citizens"
Stocks closed down 1.2 per cent, while the rate of return demanded by investors on 10-year government bonds were up at 4.520 per cent from 4.416 per cent on Friday -- an indication of investor concern.
After weeks of bickering, Berlusconi said he was pulling his party's five ministers out of the fragile coalition government with the left and called for elections as soon as possible.
But the outgoing ministers, while toeing the party line by resigning, have tried to distance themselves from Berlusconi, who has dominated Italian politics for much of the past 20 years.
Letta, a moderate leftist who only came to power this year and has struggled to boost a flagging economy, accused the three-time former prime minister of a "crazy and irresponsible" act.
The 47-year-old Letta has warned against elections at a sensitive time for Italy on the financial markets and just as the economy was hoping to shake off two years of a devastating recession.
He is hoping that members of Berlusconi's party will rebel against their weakened leader by staying in government and voting to support it in a parliamentary confidence vote on Wednesday.
