Censor.NET reports citing Reuters quoting France's Interior Minister Matthias Fekl.
The two men - 23-year-old Clement Baur and 30-year-old Mahiedine Merabet - were seized in the southern port city a few moments apart from each other on Tuesday morning.
"These two radicalized men... intended to commit in the very short-term - by that I mean in the coming days - an attack on French soil," the interior minister told a news conference.
The presidential election in France is scheduled for April 23 and May 7.
Over the past two years, more than 230 people have died in terrorist attacks organized by radical Islamists in various regions of France. With the country still under a state of emergency, Fekl said 50,000 police, gendarmes and soldiers would be deployed for each leg of the election, and security reinforced for the candidates.