Former French premier Francois Fillon contested results of his party's leadership race on Wednesday, plunging conservatives deeper into turmoil just hours after the winner said rival factions had been reconciled.
Fillon, defeated by the more hardline Jean-Francois Cope by a razor-thin margin, said an internal election committee had omitted to count votes from three overseas districts which would have tipped the result in his favor.
Furious at being beaten by a more junior rival for a post that will be a launchpad for the 2017 presidential race - Fillon said he was dropping his bid to lead the UMP and would not rule out challenging the results in court.
"The UMP cannot be built on a lie," he said on TF1 television, calling for Alain Juppe, a party veteran and ex-prime minister, to take the reins while the party seeks a way out of the impasse.
Juppe said, however, he would only do so on condition the two sides agreed to work together, which was not yet the case.
The disarray among the conservatives is providing welcome relief to Socialist President Francois Hollande and his government, which has been plagued by gaffes and a ratings plunge. Moody's downgraded French debt by one notch to Aa1 from triple-A on Monday.
Fillon's camp said he would have won by 26 votes with those extra ballots counted. As the result stands, Cope was named the center-right UMP's new leader with lead of 98 votes out of 175,000 cast.
Sunday's contest was already held up by accusations of ballot-stuffing by both candidates.
Fillon does not plan to lodge an official appeal against the results but wants the election committee which ruled in favor of Cope on Monday to reverse its decision. The committee says it cannot go back on a decision approved by both parties.
The fresh flare-up came after Cope had told a news conference he and his rival had patched up their differences in a cordial telephone chat on Wednesday morning, and both had pledged their commitment to uniting the party.
The feuding over the result looked set to deepen the antipathy between supporters of Cope and Fillon, raising the prospect of a lengthy crisis that could distract the UMP for months from its role as the main opposition party.
Cope has insisted he is the rightful leader of the party and challenged his rival to lodge an official complaint.
"We'll go to an appeals commission if we have to go to an appeals commission, and then we will look much more closely what happened in Nice," he said, referring to accusations of ballot-stuffing by Fillon's camp in the southern port city.
Cope, a disciple of ex-president Nicolas Sarkozy, was declared the winner of Sunday's vote late on Monday evening after more than 24 hours of bickering over who had won.
Fillon's campaign director, Eric Ciotti, said on Wednesday the head of the party committee which decided Monday's result told Fillon that more than 1,000 votes from party members based abroad had not been counted.
Sarkozy - whose chances of staging a comeback for 2017 will be boosted if the infighting continues - has taken pains to stay well away from the UMP debacle, slipping past journalists at a corporate event in London where he was a keynote speaker without making any comment.
(Additional reporting by Sophie Louet in Paris and Natalie Huet in London; Editing by Catherine Bremer and Sophie Hares)