The French government stepped up security nationwide Tuesday following three bloody attacks in as many days, which killed one man and injured 25.
Municipal police patrol the Christmas market in the French city of Nantes on December 23, 2014, a day after a man rammed into shoppers with his car
While the motives behind the incidents -- a knife attack on police and two cars driven into passers-by -- remain unclear, the violence has jarred nerves after repeated jihadist threats against France over its fight against Islamic extremism.
Prime Minister Manuel Valls stressed that the three incidents were "distinct" and urged the French to keep calm, while assuring that security would be heightened.
"Two hundred to 300 extra soldiers will be deployed in the coming hours," on top of the 780 troops already engaged in anti-terrorism surveillance, he said on television.
Security patrols will also be increased in shopping areas, city centres, rail stations and on public transport, he added.
The violence began on Saturday when a man was shot dead after attempting to enter a police station in the central town of Joue-les-Tours while shouting "Allahu Akbar".
The 20-year-old attacked three officers with a knife, two of whom were seriously injured.
Then on Sunday, a driver ploughed into pedestrians in Dijon in the east, injuring 13 people while also shouting the same Islamic phrase, which means "God is greatest" and has been used by extremists during violent attacks.
The 40-year-old man, who has a history of mental illness, was charged with attempted murder on Tuesday, Dijon prosecutor Thierry Bas said.
The last attack took place Monday night when a man drove his car into the middle of a bustling Christmas market in the western city of Nantes, injuring 10 people before stabbing himself repeatedly and being arrested.
A 25-year-old man later died of injuries sustained in the attack, local prosecutor Brigitte Lamy said Tuesday, adding that the injured assailant, 37, was not yet fit to be questioned.
Lamy said a notebook found in his car contained "confused" remarks about his "hatred of society" and "risk of being killed by the secret service". He also claimed his family was disparaging him on the Internet, she said.
Sources close to the investigation said he had a drinking problem and had been involved in a case of theft and receiving stolen goods in 2006.
- Don't 'give in to fear' -
Valls acknowledged that copycat attacks were possible.
"Unbalanced individuals can act. They can be receptive to, or influenced by, propaganda messages or the power of images," he said.
Authorities have for months been on tenterhooks over the threat of violence inspired by Islamic extremism.
In September, the radical Islamic State group that controls swathes of Iraq and Syria urged Muslims around the world to kill "in any manner" those from countries involved in a coalition fighting its jihadists, singling out the French.
Among instructions for killing civilians or military personnel was to run them over with a car or truck.
But while the probe into Saturday's attack is leaning towards extremist motives -- the Burundian convert to Islam who assaulted police had posted an Islamic State flag on his Facebook page -- the car rampages appeared to be the work of unstable individuals.
The prosecutors in charge of probing both incidents insisted they were not "terrorist acts".
The assailant in Dijon had been to psychiatric hospitals 157 times, local prosecutor Marie-Christine Tarrare told reporters.
She said the man told police he ploughed into people out of a sudden "outburst of empathy for the children of Chechnya" and had shouted "Allahu Akbar" to give him courage.
Lamy meanwhile said the attacker in Nantes did not appear to have a history of psychiatric trouble but that his mental state had deteriorated over the past few weeks.
"We must not panic, lump things together, give in to fear," warned President Francois Hollande on a trip to overseas French territory Saint-Pierre-et-Miquelon near Nova Scotia.
- Minimising risk? -
Nevertheless, the government faced criticism Tuesday that it was minimising the threat at a time when more than 1,000 nationals are thought to be involved in jihad on home soil, or in Syria and Iraq.
The slain assailant in Joue-les-Tours, Bertrand Nzohabonayo, was not on a domestic intelligence watch-list but his brother Brice is well known for his radical views and was arrested in Burundi soon after the incident.
Nzohabonayo's mother had told authorities last year that she was worried about Brice's radicalisation and "the influence he could have on his brother Bertrand," said Paris prosecutor Francois Molins, whose office is in charge of the probe.
The attacker in Dijon, meanwhile, had taken an interest in religion and started wearing a djellaba -- a long robe worn in Muslim countries -- just a week ago, according to his mother.