Both candidates have claimed victory in the race to become France's next opposition leader, in a contest marred by allegations of vote-rigging, BBC News reported.

Hundreds of votes are said to separate right-wing candidate Jean-Francois Cope and ex-PM Francois Fillon. As the neck-and-neck result emerged, supporters of both UMP candidates made accusations of vote fraud. The party has been without a leader since Nicolas Sarkozy was defeated in the May presidential election.

Mr Cope has been secretary general of the conservative UMP since 2010 while his rival was prime minister for five years during Mr Sarkozy's presidency.

When initial results emerged, Mr Cope was narrowly in the lead, surprising political pundits who had expected the former prime minister to win. Opinion polls had consistently given him the edge.

A UMP deputy mayor backing Mr Cope said that there had been "a certain number of irregularities" in polling stations in the Alpes-Maritimes area. In one polling station in Paris, a party official complained that there were 40 more ballots than voters on the party list.

Mr Fillon's team also registered a complaint, the BFM-TV news channel reported.

The two candidates have very different visions of the future direction the centre-right party should take. Mr Fillon, aged 58 and prime minister from 2007-12 under President Sarkozy, is seen as sober and more restrained than Jean-Francois Cope. Ten years Mr Fillon's junior, Mr Cope is considered more right wing.

The winner will inherit a party in difficult financial straits, after a series of electoral setbacks over the past five years, culminating in Nicolas Sarkozy's presidential defeat to Socialist rival Francois Hollande.