The centre-right UDI party will no longer campaign for Francois Fillon in France's presidential election after he was placed under formal investigation.

The Republican candidate has been summoned by judges investigating allegations he gave his wife a taxpayer-funded "fake job", and he said he was due to meet them on 15 March.

He denied the claims and described the probe against him as "political assassination" and vowed to stay in the race.

"I won't give in, I won't surrender, I won't pull out, I'll fight to the end," Mr Fillon said.

With just a few weeks to go before the first round of voting in the presidential election in April, Mr Fillon's support is slipping.


:: Behind Francois Fillon's surprising display of defiance

Image: The Republican's campaign hopes have been damaged by the claims

The UDI, which has about 30 MPs in the French parliament's lower house, announced its support for Mr Fillon in November, but said on Wednesday it was now "suspending" its backing.

The party leadership will meet next week to discuss whether it permanently withdraw all support for Mr Fillon.

The party's youth wing is already supporting his rival Emmanuel Macron.

Mr Fillon's statement to reporters followed a morning of speculation that he might pull out of the race.

The 62-year-old said the allegations were "entirely calculated to stop me being a candidate for the presidential election" and that the judiciary had attempted to "muzzle" voters.

However, the former prime minister said he would cooperate with the magistrates.

:: French presidential election: Who is Francois Fillon?

Image: Mr Fillon allegedly paid his wife Penelope 830,000 euros for work she did not do

Sky News Europe Correspondent Mark Stone said Mr Fillon had shown "remarkable defiance".

He said: "Every expectation was that he would fall on his sword today.

"The French media rumour mill suggested that Alain Juppe would appear alongside him - a sure sign that he was handing the reins to the man who was the runner-up in the Republican primary campaign.

"But no Juppe and no quitting - Mr Fillon was adamant that he would fight on."

Image: Far-right candidate Marine Le Pen has also been accused of handing out 'fake jobs'

He added: "(Fillon's) decision to fight on may in part be because there is literally no one able to take his place.

"Alain Juppe has repeatedly said he is 'no plan B'. And Nicolas Sarkozy, the other candidate in the Republican primary, is himself under investigation for the funding of his 2012 election campaign.

:: Far-right support keeps Le Pen in with a shot

"If Fillon pulled out and no one replaced him then voters on the right of the spectrum would have the choice only of far-right candidate Marine Le Pen or centrist former Socialist independent candidate Emanuel Macron."

Mr Fillon has lost ground in opinion polls since it was first alleged that he paid his wife Penelope €830,000 (£710,000) in public funds for work she did not do.

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Investigative magazine Le Canard Enchaine said Mrs Fillon was paid between 1998 and 2013 for working as a parliamentary assistant, but could not find any evidence of work that had been carried out.

Two of the couple's children, Marie and Charles, have also been interviewed by investigators over claims they held "fake jobs".

The polls show Mr Macron, an independent, pro-European Union candidate, consolidating his status as favourite. Far-right National Front leader Marine Le Pen is also among the leading candidates.

The top two candidates go through to a run-off held on 7 May.