* Berlusconi rebrands party under original Forza Italia name
* Centre right weakened as splinter group formed
* Tensions rise as Berlusconi faces expulsion from parliament
Silvio Berlusconi said on Saturday his centre-right party had split from Italian Prime Minister Enrico Letta's ruling coalition but said he did not have the numbers to bring the government down.
His comments came after Friday's defection of a group led by Interior Minister Angelino Alfano, former secretary of his People of Freedom party, which defied Berlusconi and formed a separate group that has pledged to remain in the government.
Speaking at a congress to rebrand People of Freedom (PDL) as Forza Italia, the name of his original political movement, Berlusconi said his impending expulsion from parliament, with the support of Letta's centre-left Democratic Party, meant the coalition could not continue.
"It's very difficult to think you can remain allies in parliament and above all seated at the same table in cabinet with someone who wants to kill your leader politically," Berlusconi told a party meeting.
Alfano's group, expected to include a couple of dozen lawmakers, should ensure enough support in parliament for Letta, who survived a confidence vote last month with the help of the PDL rebels.
"At this moment, after the decision taken by 23 of our senators on Oct. 2, we were not capable and we are not capable of bringing down the government," Berlusconi said.
The 77-year-old billionaire's political future has been in the balance since he was convicted of tax fraud in August, opening the way for his expected expulsion from parliament. The Senate is due to vote on Nov. 27 to confirm the step and the Democratic Party has said it will vote for expulsion.
Letta's Democratic Party formed an awkward coalition with the PDL following an inconclusive national election in February that left neither able to form a government on its own.
Berlusconi said Alfano's decision to form a new bloc had "caused him a lot of pain", prompting members of his audience to yell "traitors".
However, he struck a conciliatory note, urging supporters to avoid hostility towards the new grouping of his former political heir, whose tentative name will be the "New Centre Right", stressing that they should be viewed as allies.
"This group, even if it seems like it is supporting the left, will have to necessarily be part of the centre-right coalition," he said.
The billionaire politician, furious at a conviction he says was politically motivated, has been further aggravated by the rebellion, which has been the most serious threat to his authority since his entry into politics two decades ago.
The rift underscores the instability still threatening Italy, the euro zone's third largest economy, despite an uneasy truce in the coalition following Berlusconi's failed attempt to bring down Letta's government last month.