French police have said that the jihadi attack near Lyon last week was part of a wider terror operation and, as a result, Jewish institutions across the country are taking extra security measures.
Sources say that further terrorist attacks could happen at any moment and that while there are many targets, Jews and Israelis are clearly on the front line.
It is widely understood that the army, the police, industrial facilities and Christian sites also face high threat levels.
Ten weeks ago, French police arrested a jihadist who was about to attack one or several Catholic churches in the Essone area, south of Paris.
In the horrific attack near Lyon, which took place last Friday, Yassin Salih, 35, killed and beheaded his boss, Hervé Cornara, 54, at a parking lot near the Air Products chemicals factory on the edge of Saint-Quentin-Pallavier.
Posing as an Isis (Islamic State) executioner, he placed his victim's head at his feet, shot a selfie and sent it using WhatsApp to a friend who had actually joined Isis in Syria.
He then hung Mr Cornara's head on the factory's railings, between two Isis black flags.
Finally, he tried to drive a truck into a shed filled with gas bottles in order to cause a major explosion, but was intercepted by the fire brigade.
This barbaric crime prompted shock and horror across France.
The day afterwards, Libération, the liberal daily, ran the headline: "Jihad nauseam" - a pun on "jihad" and the Latin expression "ad nauseam". The National Council of the French Muslim Religion issued a formal condemnation.
The beheading occurred almost six months after the massacres at the satirical magazine Charlie Hebdo and at a kosher supermarket in Paris, which left 20 dead.
It also took place on the same day as a wave of Isis-related terror attacks in Tunisia and Kuwait.
On Friday, President François Hollande convened a special cabinet meeting to discuss the danger, and raised the security level in France to its highest possible point.
It seems that Yassin Salih had quarrelled with Mr Cornara on a work matter two days before killing him.
Mr Cornara, the manager of a delivery company, was said to be a warm and generous person but got angry with Salih when he dropped a fragile piece of equipment.
Other reports suggest Salih could have been in the middle of a domestic crisis, and that his wife had threatened to divorce him.
Nevertheless, French police say they believe that the evidence for a terrorist operation is overwhelming.
Salih, a French Muslim of north African descent, has been involved with jihadist cells since 2006. The friend to whom he forwarded the beheading selfie - named as Sébastien-Younes V - is a French-Algerian extremist who left for Syria in November, along with his wife and 18-month-old child.
Both men seem to have been influenced by Frederic Jean Salvi - also known as "Ali" or the "Great Ali" - a drug dealer who converted to Islam while in jail and subsequently organised an underground Salafist mosque in Pontarlier, eastern France - Salih's place of birth.