Former French Prime Minister Francois Fillon arrives to hold a press conference in the Musee Social. Fillon announced Tuesday that he and his followers are splitting off from France’s main conservative party and forming their own parliamentary group. (ETIENNE LAURENT/EPA)

Former prime minister François Fillon, outraged at losing a chaotic internal leadership vote marred by cheating, threatened Tuesday to split off from France’s main conservative party and take his followers into a separate parliamentary group.

Fillon said the breakaway faction could return to the mother party, the Union for a Popular Movement (UMP), if a new leadership election were held within three months to eliminate doubts as to who would assume former president Nicolas Sarkozy’s mantle as head of the right-wing opposition in France.

Fillon’s victorious rival, Jean-François Copé, had already rejected proposals for a new vote. But prodded by Sarkozy, Copé and Fillon compromised late Tuesday on an agreement to hold a referendum among the UMP faithful to see if they want to hold a second vote, probably early next year.

The fragile compromise calmed for the moment what had become an embarrassing public catfight over who was the rightful UMP president. But it left the two men arrayed in angry confrontation, with each claiming to be in charge and blaming the other for weakening the party when it should be attacking President François Hollande’s ruling Socialists.

“We are neither defeated nor are we silent,” Fillon vowed in a televised speech announcing his decision to form the dissident group, which he baptized “UMP Rally.”

The bitter wrangling between Copé and Fillon has been criticized by party activists as a ridiculous schoolyard spat that discredits the conservative movement and leaves the field open for Hollande and the Socialists.

Despite the mocking tone of many commentators, the leadership struggle has been particularly intense for several reasons. For one, Copé and Fillon have long disliked each other. Their rivalry was muted during Sarkozy’s presidency, from 2007 until May, but it broke into the open as they campaigned to become leader of the conservative movement and their party’s likely candidate for the next presidential elections in 2017.

In addition, Copé has called on the party to be right-wing “without complexes,” suggesting a hardened position on such issues as immigration and the growing Muslim presence in France. Fillon, on the other hand, dissociated himself from such appeals when Sarkozy turned to them in the final days of his losing campaign against Hollande.

Against that background, the leadership vote was also understood as a test that in large measure will determine the tone of the UMP’s opposition stands and of its presidential candidate when the next election rolls around.

Fillon’s lieutenants said that more than 60 of the 180 UMP members of the National Assembly, the lower house of Parliament, have signed up to join his new group.

Fillon emphasized he would not quit the party altogether, saying his goal was to make sure it adhered to democratic principles in its internal affairs. “We are not clan bosses,” he added, seeking to discredit Copé’s leadership and the tactics he has used to defend the widely contested Nov. 18 vote.