French police have arrested a man suspected of planning an attack on "one or two churches", the country's interior minister has said.
The man, a 24-year-old Algerian national, was detained on Sunday in Paris after he apparently shot himself by accident and called an ambulance.
He is also being questioned over the murder of a woman on Sunday.
France has stepped up security in the wake of recent attacks on the Charlie Hebdo offices and a Jewish supermarket.
The man was known to security services as having expressed a wish to travel to Syria, French Interior Minister Bernard Cazeneuve said.
When police arrived at the scene on Sunday, they followed a trail of blood to the suspect's car, where they found weapons and notes on potential targets.
The documents established "beyond doubt that the individual was planning an imminent attack, probably on one or two churches," said Mr Cazeneuve.
"Several war weapons, hand guns, ammunition [and] bullet-proof vests," were found in his car and home, the minister added.
The authorities have carried out security checks on the suspect twice in recent years but did not uncover anything to justify further investigation.
VictimIt is not known yet what link the man has to the murdered woman, Aurelie Chatelain, who was found dead in her car in a Paris suburb on Sunday.
Passers-by discovered her body as smoke poured out of the car from an overheating laptop.
The 32-year-old was visiting the Paris area to attend a training course.
"Our thoughts and sorrow are with her relatives, her family, and her daughter now deprived of her presence." said Mr Cazeneuve.
Hundreds of French citizens have travelled to Syria and Iraq to fight alongside militants, with many at home with links to recruitment cells.
There was no immediate evidence the suspect had links to organised groups, a French security official told AP.
"Terrorists are targeting France to divide us," French Prime Minister Manuel Valls warned on Wednesday.