Italian PM Enrico Letta has been addressing parliament ahead of a crucial vote of confidence in his governing coalition.
Enrico Letta told the Senate the collapse of his government could be fatal for the country.
The vote was called after former PM Silvio Berlusconi ordered ministers in his centre-right People of Freedom party (PDL) to leave the government.
But some key PDL figures have defied him, saying they will back Enrico Letta.
Enrico Letta earlier rejected the resignations of the five PDL ministers.
Silvio Berlusconi has accused Enrico Letta of allowing his “political assassination through judicial means” – a reference to Berlusconi’s criminal conviction for tax fraud in August.
“Even though I understand the risks that I am taking on, I have decided to put an end to the Letta government,” Silvio Berlusconi said in a letter to the weekly magazine Tempi.
However, Silvio Berlusconi appeared more circumspect on arrival at the Senate on Wednesday, saying: “We’ll see what happens. We’ll listen to Letta’s speech and then we’ll decide.”
Addressing the Senate, Enrico Letta defended his government’s performance and said Italy “runs a risk, a fatal risk” if it were to fall.
He said: “Give us your confidence to realize [our] objectives. Give us your confidence for all that has been accomplished… a confidence vote for Italy and Italians.”
In an apparent break with Silvio Berlusconi, his deputy and party secretary Angelino Alfano said PDL MPs should back Enrico Letta in the confidence vote.
“I am firmly convinced that our party as a whole should vote confidence in Letta,” said Angelino Alfano, who is also Italy’s interior minister.
The first vote on Wednesday is in Senate and is expected around midday. This will be the crucial moment, as it is where Silvio Berlusconi’s allies have a narrow majority. The chamber of deputies will vote later.
Enrico Letta needs 161 votes in the Senate but can only count on the support of about 137 members, meaning he will need about 25 votes from others.
There are reports that between 30 and 40 PDL senators may vote for the government.
Angelino Alfano’s comments had caused the Italian stock market to jump on Tuesday as investors appeared increasingly confident that the government would not fall.
Carlo Giovanardi, a senator from Silvio Berlusconi’s party, indicated he would support the government, adding: “We want to remain a moderate force.”
Fabrizio Cicchitto, a PDL deputy, said: “Making the government fall would be a mistake.”
He said any new government would be “hostile to the PDL” and would be a boon for Enrico Letta’s centre-left Democratic Party.
On Tuesday, Enrico Letta refused to accept the resignations of five ministers from the PDL, Italy’s Ansa news agency reported, citing a government source.
Enrico Letta called the vote of confidence after Silvio Berlusconi ordered his ministers to leave the government in protest at a rise in VAT (sales tax).
The prime minister accused Silvio Berlusconi of using the issue as an “alibi” for his own personal concerns.
Analysts say the crisis threatens to hamper badly needed reforms to tackle Italy’s economic problems that include debt, recession and high youth unemployment.
The International Monetary Fund has warned that political tensions are a risk to the Italian economy.
Enrico Letta’s cross-party alliance was formed in April after two months of political deadlock following an inconclusive election.