By Nicholas Vinocur
PARIS (Reuters) - French conservative Jean-Francois Cope shattered a short-lived truce on Wednesday in the dispute over his victory in a leadership election last week, thrusting the party of former president Nicolas Sarkozy deeper into crisis.
Members of the UMP opposition party had breathed a sigh of relief on Tuesday when Sarkozy stepped in to mediate a deal, getting the warring factions to agree to hold a referendum on whether to repeat the contested November 18 vote.
Despite rival Francois Fillon's move to form a separate parliamentary group in recent days, Cope had initially said on Tuesday evening he would accept the deal.
But interviewed on French radio on Wednesday, he said a referendum could not be held as long as Fillon persisted with the plan for a breakaway wing.
"The red line has been crossed and I draw the consequences from that," Cope told Europe 1 radio. "I don't believe the conditions are in place (to hold a referendum)."
Sarkozy, who had kept a low profile since losing a re-election bid in May and vowing to quit politics, has re-emerged on the scene as the only man able to save the party he led before being elected president in 2007.
As the truce unraveled, members of Sarkozy's entourage told French media that he was unlikely to make a public statement.
The crisis over finding a successor to the former president has brought the normally disciplined center-right UMP back to an era of warring factions and mutual suspicion ten years after it was formed to unify fractious right-wing currents.
While Fillon, who sits at the center of his party, and the more hard-right Cope have both said they want to keep the UMP intact.
Fillon, who was a popular prime minister under Sarkozy, said his breakaway group would rejoin the UMP and drop all legal procedures disputing the vote if parties reached a deal on how to hold a referendum.
An independent commission would have to guarantee a clean vote and equal terms, he said in a statement.
For Cope - who has repeatedly declared victory, most recently after an adjusted ballot count by the party's internal appeals commission gave him a 952-vote lead over Fillon - it was a signal to tighten his grip on the party.
"This is not going to work," said one of his supporters at the party headquarters, asking not to be named. "If they want to go to the courts, then let them."
With the UMP's woes overwhelming all political coverage on three 24-hour news channels, even members of President Francois Hollande's Socialist government were pleading for it to end.
"It's no reason to smile because in reality, people are fed up - we have the feeling that this is more about a war of egos," Foreign Minister Laurent Fabius told France Inter radio.
Far-right leader Marine Le Pen told Reuters the UMP's crisis was an opportunity to position her National Front as the country's foremost opposition party. She says requests to join her party have shot up in recent days.
"All of this... should be a reason to be hopeful because it allows us to lay the groundwork for a new era," she said.
(Additional reporting by Sophie Louet, Gerard Bon and John Irish; Writing by Nick Vinocur; Editing by Catherine Bremer and Patrick Graham)