A 'radicalised' ex-soldier with an ISIS flag in his car has been arrested at a military airbase near Paris after guns and ammunition were discovered nearby, just two days before the country's presidential election.

French authorities found an allegiance pledge to the Islamic State group, a copy of the holy Quran book and several flags in the car of the suspected radical, sources said.

The pledge was on a flash computer drive in his vehicle, which was parked close to Évreux-Fauville airbase near Paris. Guns were also found hidden in bushes near the facility.

Suspect: French authorities found an allegiance pledge to the Islamic State group and several of its flags in the car of the suspected radical close to Évreux-Fauville airbase, pictured above, close to the country's capital Paris

Local media reported a 34-year-old former serviceman was arrested at around 5.30am this morning and has been taken into police custody.

The alarm was raised after locals became suspicious of a car parked near the site at around midnight on Friday.

Police arrested the man and according to sources close to the case, found ISIS flags, a copy of the Quran and a pledge to extremist group IS.

The man is understood to be on the French watchlist for extremists.

Paris anti-terror prosecutors are investigating, but it is not clear why the suspect was near the base as he is no longer serving in the military.

French voters head to the polls Sunday to pick their next president in a bruising and divisive campaign overshadowed by security worries.

Karim Cheurfi, a 39-year-old Frenchman, shot and killed a police officer and wounded two others on the Champs Elysees avenue days before the first round of voting, in an attack claimed by the Islamic State group.

Cheurfi was killed in return fire.