French presidential frontrunner Emmanuel Macron has filed a formal complaint against rival Marine Le Pen after she implied he had an offshore bank account in the Caribbean.

Le Pen made the implication that Macron was avoiding taxes in the televised debates on Wednesday (3 May) during a head-to-head that was filled with personal attacks and fiery rhetoric.

It followed from apparent forgeries published online hours before the debate linking Macron to a bank on Nevis island.

Speaking during the debate, Le Pen said she hoped "we will not find out that you have an offshore account in the Bahamas" as she was eager to bring up his banking past and accused him of being a puppet of global financiers.

Macron quickly dismissed the suggestions as "defamation" and a member of his camp later said: "We will not hesitate to prosecute for defamation anyone who repeats this false information."

Speaking on France Inter radio, Macron said: "I've never had an account in any tax haven. Le Pen is behind this. She has an internet army mobilising."

Le Pen backtracks on claim

The far-right leader, who had eggs thrown at her by a small group of protestors as she campaigned in Brittany, denied accusing Macron of having offshore bank accounts.

"Not at all," she told BFMTV. "If I wanted to do so, I would have done it yesterday.

"I've just asked him the question. If I had proof, I would have claimed it yesterday."

Paris prosecutors have reportedly launched a preliminary investigation into whether fake news played a part in the televised debates.

Despite the implications, pollsters said roughly 60% of viewers believed Macron won the debate – a finding similar to the predicted outcome in Sunday's second-round of voting.