The probe will examine allegations by three members of the far-left La France Insoumise (France Unbowed) that they faced smear campaigns of false accusations, social media manipulation and fake campaign visuals.

They include Sebastien Delogu from Marseille in the south and Francois Piquemal in Toulouse in the southwest, who lost their election bids, and David Guiraud in Roubaix in the north, who won the vote to become mayor.

“You get in your car and you see a billboard with your name and a QR code that links to false accusations of rape,” Delogu told reporters last week.

Piquemal said his campaign faced “the creation of pages on social networks spreading the worst rumours”, along with the publication of his social media passwords.

The trio said they were targeted because of their support for the Palestinian cause.

The case was opened after Viginum, France’s government body responsible for combatting online disinformation, said that it had noted a “system of artificial or automated dissemination to spread manifestly inaccurate or misleading content”.

“This malicious campaign, involving an actor located abroad, is liable to undermine the fundamental interests of the nation, insofar as it deliberately seeks to distort citizens’ access to information,” the agency said.

A source connected with the case told AFP that the campaigns appeared to be conducted from Israel, with two left-leaning dailies — France’s Liberation and Israel’s Haaretz — naming companies that were allegedly responsible.

AFP was not immediately able to confirm the reports.

Prosecutors said that up to now they have not seen indications that the Israeli government was involved.

“The notion of interference does not concern the interests of a foreign individual or company, but of a foreign state, and no suspicion of such an intervention… has been reported.”