The French prosecutor's office has launched an inquiry into suspicions of fake news being spread to influence Sunday's presidential vote after far-right leader Marine Le Pen implied her rival Emmanuel Macron held an offshore account.
Mr Macron, favourite to win the presidency, denied allegations of using a foreign tax haven that were made on social media and referred to by Ms Le Pen in an ill-tempered televised debate with him last night.
He accused her of spreading lies.
After Mr Macron lodged a legal complaint over the allegations, a judicial source said the prosecutor's office was investigating suspicions that fake news had been intentionally circulated with the aim of swaying Sunday's voting.
Opinion polls show Mr Macron, a centrist, has roughly a 20 point lead over Ms Le Pen.
They see him firmly on course to winafter what was widely seen as his solid performance in the fractious face-to-face.
French shares and bonds and the euro performed strongly today, pointing to relief on financial markets that Ms Le Pen had not gained ground with her pledges to quit the euro, hold a referendum on leaving the European Union, and print money to finance higher state spending.
It was at the end of the two-and-a-half hour debate, watched by 15 million people, that the National Front veteran insinuated that Mr Macron might be concealing funds on a foreign tax account.
"I've never had an account in any tax haven," Mt Macron told France Inter radio. "Le Pen is behind this. She has an internet army mobilising."
He said she had allies spreading "false information and lies" who were "in certain cases linked to Russian interests".
Mr Macron's party has previously complained that his campaign had been the target of "fake news" put out by Russian media, as well as internet attacks on its databases.
That prompted a warning by the French government in Februar ythat it would not accept interference by Russia or any other state in the election.
According to a snap poll by Elabe for BFMTV, 63% of viewers found Mr Macron the more convincing of the two candidates in thes debate, reinforcing his status as favourite to win.
A second poll by Harris Interactive said 42% of people found Mr Macron more convincing in the debate, during which the candidates traded barbs over the economy, the euro and how to combat terrorism.
26% found Ms Le Pen more convincing, while 31% chose neither candidate, Harris said.
Meanwhile former US President Barack Obama endorsed Mr Macron in a video message released by Mr Macron's party, praising him for appealing "to people's hopes and not their fears".
