One of the three suspects, the youngest of whom is just 17, was allegedly in contact with an Islamic State militant in Syria, who had told them to “strike in France”. He has also made a statement from the Elysee Palace on his immediate return, announcing that France’s national security will remain at the highest alert level.

President Francois Hollande said Wednesday during a visit to the southern city of Marseille that several terrorism attacks were foiled this week, without providing details.

French authorities have foiled a plot by four would-be extremists to attack military bases, the interior minister has said.

“You cannot stop that message getting out, all you can do is to see the reaction in time”.

The judicial official said the plot centered on an attack on Fort Bear with plans to decapitate an officer and film the scene, mimicking the grisly killins of the Islamic State group in Syria and Iraq, a scenario confirmed during interrogation.

According to the local media, the four individuals are suspected of plotting terrorist attacks in French departments of Bouches-du-Rhone, Rhone and Yvelines.

At traditional July 14 celebrations, Hollande said: “Every week, we are arresting, preventing… terrorist acts”. Another policewoman was also killed by the suspects. “The first indications show that we are dealing with a criminal act, but no motive has been established”, Cazeneuve told the lower house of parliament.

Cazeneuve said there was no terrorist link so far determined with a suspected arson case that caused two explosions at a chemical factory in the south of the country on Tuesday.

Authorities are still investigating the simultaneous blasts that hit two tanks containing chemicals early Tuesday, setting off huge fires at the plant in Berre-l’Etang, northwest of Marseille, as mentioned by CNN affiliate BFMTV.

No weapons were found during the arrests, the source said, although officials discovered documents on preparing explosives.

France, which is home to Europe’s largest Muslim population, has beefed up security, posting 30,000 police officers and soldiers outside 500 sites deemed “sensitive” such as schools and places of worship.

But experts warned it was extremely difficult to defend against attacks on such sensitive sites.

“We have to realise that we have been in a fundamentally different environment for the past three years”.