French police on Tuesday arrested two men suspected of preparing an "imminent" attack, authorities said just days ahead of the first round of France's presidential vote.
The suspects, aged 23 and 29, were taken into custody by French domestic intelligence service agents in the southern city of Marseille, a source close to the probe said.
French Interior Minister Matthias Fekl said the "radicalised" men intended to strike "in the next few days in France", but provided few details about the alleged plot.
France has remained on high alert since a string of terror attacks that began in 2015, which have killed over 230 people.
Polls have shown that voters are more concerned about unemployment and their spending power than terrorism or security, though analysts warn this could change quickly in the event of further bloodshed.
Anti-EU, anti-immigration candidate Marine Le Pen has sought to cast herself as the best defender of France against the threat of fresh attacks.
Le Pen and Emmanuel Macron, the 39-year-old europhile given the best chance of beating her in a run-off, are leading in opinion polls for the first round of the election on April 23, with around 22 to 24 percent each.
Radical leftist candidate Jean-Luc Melenchon and conservative ex-premier Francois Fillon have gained ground, transforming the election into a tight four-way race. The two leaders of the first round will go through to a run-off on May 7.