Former French President Nicolas Sarkozy (2nd L) enters his car as he leaves his house in Paris.

Paris - Ex-president Nicolas Sarkozy was set on Monday to wade into a bitter leadership battle that is threatening the future of France's main right-wing opposition party, the UMP.

The political heir of the party founded by Charles de Gaulle after World War II was on the verge of collapse after accusations of vote-rigging tarnished a leadership vote.

Still reeling from its loss of the presidency and parliament this year, the UMP is facing the spectre of an unprecedented split on the right, with rival camps showing no sign of backing down in an increasingly angry dispute.

Sarkozy was to meet one of the rivals for the leadership, his former prime minister Francois Fillon, for lunch after flying in early Monday from a conference in Shanghai, a source close to Fillon said.

The meeting comes after talks to resolve the damaging dispute collapsed late Sunday.

Called in to mediate, party heavyweight Alain Juppe threw in the towel after less than an hour of talks between Fillon and his rival, ambitious party secretary general Jean-Francois Cope.

Juppe said Monday that only Sarkozy would be able to resolve the crisis.

“I used to think the former president should protect himself a bit from this partisan bickering,” Juppe told RTL radio. “Clearly he is the only one today to have enough authority to propose a way out.”

Fillon, 58, and Cope, 48, have traded accusations of fraud and ballot-rigging since last Sunday's party election ended with Cope ahead by only 98 votes.

The party electoral commission has since said that ballots cast in France's overseas territories that were not counted would have reversed the result, while the Cope camp has claimed he would have won by a clear margin but for vote-rigging in the Mediterranean city of Nice.

Fillon said Cope was to blame for the failure of the mediation efforts and announced he would turn to the courts to resolve the dispute -- a move UMP vice-president Luc Chatel described as a “nuclear bomb” inside the party.

On Monday, Fillon stepped up the battle by calling for the “precautionary seizure” of ballots cast in the leadership vote “to protect them from tampering or alteration”.

A party appeals commission resumed meeting on Monday to deal with complaints of vote irregularities, but Fillon's camp walked out of such a meeting on Sunday and has accused the commission of pro-Cope bias.

The party has faced ridicule over the debacle at a time it could be taking advantage of Socialist President Francois Hollande's falling popularity over his handling of France's struggling economy.

Pro-right newspaper Le Figaro said on its front page Monday that the party was committing suicide, headlining an editorial, “Stop the Massacre!”

But the UMP's opponents were already writing its obituary, with Marine Le Pen, the leader of the far-right National Front, saying: “The UMP no longer exists. The UMP is dead.”

Fillon supporters have already raised the prospect of a split in the UMP's parliamentary faction - a move that could deprive the party of crucial funding and credibility.

The UMP has 183 members in France's 577-seat lower house National Assembly, the second-largest group after the Socialists.

Polls show the overwhelming majority of French voters and UMP supporters would like to see the party run the election again as a way out of the crisis.

But Cope has repeatedly rejected the idea and urged the UMP to unite under his banner.

Asked about a new vote on Monday, he said: “It is not that I don't want one, it's that it would be irresponsible.

“The election has taken place. ... If there happens to be fraud observed in a small fraction of the electorate, we aren't going to ask everyone to vote again.” - AFP