Presidential hopeful Emmanuel Macron has filed a legal complaint after his far-right rival Marine Le Pen accused him of holding money in a tax haven.

The 39-year-old ex-economy minister described his rival's insinuation as 'defamation' and after his complaint, French prosecutors launched a probe Thursday into who started the rumour.

Macron's campaign team called it a 'textbook case' of 'fake news', saying it was spread on Twitter by accounts close to Kremlin-friendly news sites like Sputnik and RT as well as supporters of US President Donald Trump.

Miss Le Pen, 48, later admitted to French television channel BFMTV that she had no evidence to back up her comments but had read about the allegations. It came after fake documents purporting to relate to overseas bank accounts were shared on social media.

Presidential hopeful Emmanuel Macron has filed a legal complaint after his far-right rival Marine Le Pen accused him of holding money in a tax haven

After accusing the Front National (FN) candidate of 'defamation' on live television on Wednesday night, Mr Macron, 39, filed a complaint with the state prosecutor about the rumours, claiming that an online 'fake news' campaign had been mounted to influence voting.

He said Miss Le Pen was behind the rumours, telling French radio: 'She has an internet army mobilising', adding that she had spread 'false information and lies'.

He also said some of the sites spreading the allegations were 'linked to Russian interests'.

An aide for Mr Macron said the party would sue for defamation if the false allegations were repeated.

The dramatic twist came after 15 million viewers tuned in to a two and a half hour debate which was widely regarded as the most brutal in French political history and likened to the standoff between Hillary Clinton and Donald Trump.

French media described 'unprecedented brutality' and said the showdown had 'descended into chaos'.

He accused the Front National (FN) candidate of 'defamation' on live television on Wednesday night after her remarks

But despite the vicious attacks on Mr Macron, many believed he had won the debate with a snap poll by Elabe for BFMTV finding that 63 per cent saw him as the clear victor.

During the stand-off, Miss Le Pen also took the opportunity to take a swipe at Mr Macron's private life, joking: 'I can see that you are trying to do a 'pupil teacher' (scenario). That's not really my thing! And I can tell you, you are not particularly my thing!'.

She was referring to Mr Macron's marriage to his former teacher, Brigitte Trogneux, 64, who is more than 24 years his senior.

Miss Le Pen accused her rival of being the candidate of 'savage globalisation' and vowed to pull out of the euro if elected, adding: 'The euro is the currency of bankers, it is not the currency of the people'.

Mr Macron meanwhile said that leaving the euro would be 'dangerous' and branded Miss Le Pen the 'high priestess of fear'.

Emmanuel Macron (pictured at a rally in Albi, southwestern France) is currently the clear favourite to win the election

The pair also clashed on the issue of terrorism with Mr Macron telling Miss Le Pen that her scaremongering was playing into the hands of terrorism. Miss Le Pen fought back telling him he had no terror programme which 'stood up'.

Former US President Barack Obama also weighed into the debate, pledging his support for Mr Macron in the second round of the elections on Sunday.

In a message posted on Twitter, Mr Obama said he was endorsing Mr Macron, a centrist who created party En Marche! last year because 'of how important this election is'.

Mr Obama said: 'I'm not planning to get involved in many elections now that I don't have to run for office again, but the French election is very important to the future of France and the values that we care so much about.'

He continued: 'I have admired the campaign that Emmanuel Macron has run. He has stood up for liberal values. He put forward the vision for the important role that France plays in Europe and around the world.

'And he has committed to a better future for French people. He appeals to people's hopes and not their fears.'

Former US President Barack Obama also weighed into the debate, pledging his support for Mr Macron in the second round of the elections on Sunday

But while Mr Macron enjoyed support from the former president, Miss Le Pen was pelted with eggs as she visited voters in Brittany.

Miss Le Pen, who reached to protect her head, narrowly missed finding herself with egg on her face as the protesters shouted: 'Fascists get out' and 'You shouldn't be here Madam,'

The mother-of-three was also blasted by her father, former FN leader Jean-Marie, 88, who said she 'lacked gravitas'.

In the wake of Wednesday night's debate, French shares and bonds rallied.

The French will go to the polls on Sunday night to determine who will be the next leader. The result will have a major impact on Britain's Brexit negotiations, with Mr Macron promising to strengthen the EU while Miss Le Pen has threatened 'Frexit' if elected.