A man allegedly planning an attack on "one or two churches" has been arrested in Paris, France's interior minister announced, adding that the IT student was also allegedly behind the murder of a woman near the French capital.
The 24-year-old, who was detained on Sunday, was known to intelligence services for wanting to go to Syria to fight against the Syrian government.
"Several war weapons, hand guns, ammunition, bullet-proof vests and computer and telephone hardware" were found at his home and in his car, Interior Minister Bernard Cazeneuve said on Wednesday.
The arrest comes more than three months after Muslim gunmen went on a three-day killing spree in and around Paris, leaving 17 people dead.
The January 7-9 attacks on Charlie Hebdo magazine, a policewoman and a Jewish supermarket sent shockwaves around the world, and prompted several reforms in France including controversial new spy laws that are currently being debated in parliament.
Cazeneuve told reporters that apart from the weapons, police had also discovered detailed research "clearly establishing that the person was planning to commit an imminent attack against one or two churches".
"Sunday morning, this attack was foiled."
French Prime Minister Manuel Valls warned that terrorists were trying to divide the country.
"Terrorists are targeting France to divide us and our response must of course be to protect citizens but also to rally together, unite and to be hugely determined faced with this terrorist threat," Valls said on French television.
The suspect's alleged link to the murder of Aurelie Chatelain was not clear. Her body was discovered on Sunday in her car in Villejuif, a town close to Paris. She had been shot three times.
The 32-year-old mother had just come to the area from northern France to take a pilates training course and had written of how happy she was to be there on her Facebook page on Saturday evening.
About nine hours later, her body was discovered by passers-by as smoke poured out of the car from an overheating laptop.
The car was parked in a turn in the road, on a hill, in front of another vehicle in a calm residential road.
A judicial source told the AFP news agency on Sunday that investigators were still searching for the motive behind the killing.
The French capital is still under maximum alert following the January attacks, and Cazeneuve reiterated on Wednesday that the country was faced with an "unprecedented terrorist threat".
Hundreds of French nationals have left France to join armed groups in Iraq and Syria, where they represent almost half the number of European fighters present, according to a report released this month by the upper house Senate.
Authorities are concerned that these nationals will come back and commit attacks on home turf.