PARIS French prosecutors opened an investigation on Friday into written death threats posted along with bullets to two news outlets and several magistrates, officials said.
Mediapart, an investigative online publication and one of the two news organisations targeted, said it and Le Canard Enchaine, a satirical weekly which specialises in lifting the lid on political scandal, had both received identical letters from a group calling itself "The Purge Collective 2J".
The 2J appeared to be a reference, below a sketch of a coffin, to judges and journalists.
The prosecutor's office would not confirm a Mediapart report that the magistrates targeted were four of those investigating conservative presidential candidate Francois Fillon.
Fillon, a 63-year-old ex-prime minister, is being formally investigated by financial prosecutors on suspicion of fraud in a scandal, first disclosed by Le Canard Enchaine, which has badly hurt his campaign for the elections on April 23 and May 7.
A copy of the letter, tweeted by Mediapart, and which also showed a bullet, said that "vigilance and protection" did not last forever. "When that day comes, we will be there for you or one of your loved ones," it said above a skull-and-cross bones.
Reporters Without Borders, an organisation which promotes press freedom, issued a statement condemning the threats and said these should be taken very seriously by the authorities.
Referring to what it described as a "poisonous" atmosphere around the election in which journalists have come under fire for political muck-raking, including from Fillon and far-right National Front chief Marine Le Pen, it said: "These acts of intimidation are unacceptable in a democracy."
Fillon particularly has criticised the media, which disclosed the scandal involving payments of public funds to his wife and children, and accused the judiciary of being unfairly biased against him.
In January 2015, two Islamist gunmen stormed into the Paris headquarters of the satirical magazine Charlie Hebdo and opened fire, killing 12 people including several members of the editorial team, and injuring 11 others.
(Reporting by Jean-Baptiste Vey; writing by Richard Balmforth; editing by Ingrid Melander/Mark Heinrich)