US whistleblower Edward Snowden is among 500 leading artists and activists to have signed the open letter in support of Le Monde
US whistleblower Edward Snowden is among 500 leading artists and activists to have signed the open letter in support of Le Monde GETTY IMAGES NORTH AMERICA / Phillip Faraone

Around 500 leading writers, artists and activists, including US whistleblower Edward Snowden and novelist Salman Rushdie, on Friday signed an open letter supporting reporters at French daily Le Monde in their battle for guarantees of editorial independence.

France's centre-left paper of record has been plunged into turmoil by the failure of Czech energy billionaire Daniel Kretinsky, who bought a stake in the broadsheet last year, to sign an agreement on the paper's editorial freedom.

The journalists have given him until September 17 to sign the accord.

"At this time when even facts are being challenged, the liberty and independence of the press are more precious public assets than ever," the open letter published on the website of Le Monde read, warning that the paper's editorial freedom was "under threat."

Kretinsky last year bought a 49-percent stake in a holding company owned by Matthieu Pigasse, one of Le Monde's biggest shareholders.

The deal gave him a stake in the daily created just after the liberation of Paris in World War II at the request of wartime leader Charles de Gaulle.

His arrival sparked concern among a group of Le Monde journalists, readers, staff and founders that oversees the paper's independence, with some expressing fears he could try influence the paper's reporting on the environment.

The "independence pole", as the group is known, is demanding to right to veto any controlling shareholder of the paper.

One of the paper's two major shareholders, French tech billionaire Xavier Niel, has already signed the agreement but Pigasse and Kretinsky have yet to do so.

Kretinsky has been on a French media buying spree recently, acquiring news weekly Marianne and other popular titles such as Elle magazine.