On Tuesday, French police arrested two men in Marseille, south France, on suspicion of planning "an imminent and violent act on French territory", on the eve of presidential election.
With four days until Sunday's first round of the presidential election, candidates blanketed the country ahead of the nail-biting election.
French authorities found guns and bomb-making materials during searches in Marseille.
In their Marseille apartment police found one automatic rifle, two handguns, quantities of ammunitions and three kilograms of explosives as well as products and equipment to make explosives, Molins said.
Le Monde reported that security forces had strengthened security measures for the rallies of several candidates, including Fillon, far-right leader Marine Le Pen and centrist Emmanuel Macron, in recent days.
A source close to the investigation said on Wednesday that the candidate featured on the newspaper cutting was Fillon.
Candidates on the far right have used their campaigns to appeal to voters traumatised by IS-inspired attacks that have killed at least 235 people in France since January 2015, the largest casualty rate of any Western country.
France remains in a state of emergency and on high alert over possible terrorist attacks.
Candidates have been heavily guarded during the election campaign, but so far there have been few security scares.
The presidential race has narrowed with just days to go, with the pack closing behind frontrunners Macron and Le Pen.
Opinion polls predict that Macron and Ms Le Pen will reach the second round on 7 May.
Some analysts have also depicted the French election as a sort of referendum on the European Union, with Le Pen proposing to pull France out of the 28-member club and scrap the euro common currency.
The outcome is likely a second round run off that would pit Le Pen, Macron, Melenchon or Fillon against one another in a number of combinations.
Le Pen's deputy Florian Philippot fired back: "You'll see, we'll soon be sticking your oligarchic rag in the cupboard".
Independent centrist candidate Emmanuel Macron, who was at the top of a recent poll, reached out to the Muslim community for solutions.
Le Pen also said she would issue an order to freeze long-term visas for a two-week period so the government can verify, among other things, that the recipients aren't taking jobs away from French citizens.
The arrests come five days before the French go to the polls in the most uncertain French presidential election in the country's recent history - nearly a third of the electorate is still undecided and the four front-runners are clustered around 20 percent in the polls for the first ballot. About one-third of eligible voters remain undecided.
Conservative candidate Fillon said "democracy must not get on its knees in front of the threats and intimidations from terrorists".
"The behavior of people who are now planning not to vote is a major factor".
Having led polls at the turn of the year, the scandal hit his support hard.
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