Attacks show threat to France

• Weekend terror attacks -- plus an incident Monday in Nantes -- have France on edge


• The threat of a terrorist attack in the EU is greater than at any time since 9/11, officials say


• Support for ISIS runs deep among disenfranchised immigrant communities

(CNN) -- A 20-year-old French-Burundian posts the ISIS flag on his Facebook page, then enters a police station in the suburbs of Tours on Saturday, shouts Allahu Akbar and slashes one officer across the face with a knife and wounds two others before a fourth officer shoots him dead.

A 40-year-old French-North African with a long history of psychiatric problems shouts the same words on Sunday as he plows his Renault Clio into pedestrians in five locations in Dijon, injuring 11 people -- two seriously -- before being arrested after a police chase.

A man drives his car into a Christmas market in Nantes on Monday then stabs himself, leaving 10 injured in an incident authorities say has not been linked to terrorism.

The two attacks over the weekend -- and the incident still being investigated in Nantes -- have rattled nerves in France.

European officials tell CNN the threat of terrorist attack in the European Union is greater than at any time since 9/11 because of the emergence of jihadist safe havens in Syria and Iraq. But no country faces a greater terrorist threat than France, with support for ISIS running deep among disenfranchised immigrant communities in the rundown, crime-ridden banlieus that surround many French towns.

French Prime Minister Manuel Valls on Monday said his country had never faced a greater terrorist threat.

The numbers tell the story: 390 French extremists are now fighting with jihadist groups in Syria and Iraq, according to French officials, with 231 believed to be on their way. Fifty-one have been killed in suicide bombings and combat. And 234 have left the conflict zone, with 185 now back in France.

Since the summer of 2013, French police say they have thwarted five terror plots.

Neither of the weekend attackers traveled to Syria or Iraq. The deceased Tours knife attacker -- a convert named Bertrand Nzohabonayo -- appears to have been a lone wolf inspired by but not directly connected to ISIS. According to French media reports, his brother had been on the radar screen of French security services, suspected of wanting to wage jihad in Syria.

In a news conference on Monday, the local prosecutor in Dijon said the attack in his city the previous day was "absolutely not a terrorist act" citing the suspect's mental health history, but French authorities might yet open a terrorism investigation.

ISIS threats to France

ISIS has explicitly called for lone-wolf terrorist attacks in France because of its participation in airstrikes in Iraq by the U.S.-led coalition, and the weekend attacks were eerily similar to the methods they suggested.

"If you are not able to find an IED or a bullet, then single out the disbelieving American, Frenchman or any of their allies. Smash his head with a rock or slaughter him with a knife or run him over with your car or throw him down from a high place or choke him or poison him," ISIS spokesman Abu Muhammad al Adnani stated in an audiotape in September.

On November 19, three French ISIS fighters appeared in a French language video put out by the group's propaganda arm, repeating the call for attacks in France. One of them stated:

"Terrorize them and do not allow them to sleep due to fear and horror. There are weapons and cars available and targets ready to be hit. Even poison is available, so poison the water and food of at least one of the enemies of Allah. Kill them and spit in their faces and run over them with your cars. Do whatever you are able to do in order to humiliate them, for they deserve only this."

A significant number of the nearly 400 French nationals now fighting in Syria and Iraq are believed to have joined ISIS. That includes Maxime Hauchard, a 22-year-old convert from Normandy who French authorities suspect participated in the grisly on-camera beheading of more than a dozen members of the Syrian armed forces in November orchestrated by the British "Jihadi John."

French officials are worried that those on their way back to France -- or already back in the country -- could launch attacks.

In February, police in Cannes broke up an alleged plot to bomb targets in France by Ibrahim Boudina, a French-Algerian extremist who had allegedly just returned from fighting with ISIS in Syria. Police say they found almost a kilogram of the high explosive TATP in his family apartment building in Cannes. Boudina has denied the allegations against him.

ISIS-linked terror on the French Riviera

Mehdi Nemmouche, a French-Algerian ISIS fighter who allegedly helped guard Western hostages in Syria before returning to Europe, allegedly shot and killed four people at a Jewish museum in Brussels in May.

Nemmouche was arrested in France and extradited to face trial in Belgium. He has denied the charges. In both the Cannes and Brussels plots, investigators believe it is possible the men were acting on their own steam. No evidence has been publicly released suggesting ISIS leadership signed off on the plots.

It is not just ISIS causing concern to French security officials. European counterterrorism officials tell CNN a relatively high number of French extremists have joined ISIS rival Jabhat al Nusra, al Qaeda's affiliate in Syria.

Of most concern: David Drugeon, a French covert from Brittany who has emerged as one of the most skilled bombmakers in the Khorasan group, an al Qaeda A-team based in Syria's Idlib province with ties to Jabhat al Nusra.

U.S. officials tell CNN they believe Drugeon has been working on nonmetallic explosive devices that the group hoped to smuggle on board Western passenger aircraft and has been talent-spotting European extremists in Syria who can be trained for attacks in Europe. Drugeon was injured in a U.S. drone strike that hit a vehicle he was traveling in November.

Khorasan bomb maker thought dead survived

New laws, old grievances

In November, France adopted tough new anti-terror legislation making it easier to shut down jihadist websites and confiscate passports and identity cards of those suspected of wanting to travel overseas to fight jihad.

But critics say the French government has done too little to tackle one of the key contributing factors to radicalization: The deep sense of alienation toward mainstream society felt by a significant number of young Muslim immigrants in the banlieus.

In the years after 9/11, France was held up as a model by many for its "assimilationist" agenda and its zero tolerance of extremist radical preachers. Britain, by contrast, was criticized for a "multicultural" approach that for too long offered political refuge to extremists from around the world.

But by the late 2000s, Islamist extremism had also become a significant problem in France. Although French leaders paid lip service to assimilation, the concept was only theoretical for young unemployed Muslims living in impoverished banlieus whose socioeconomic grievances were more acute than their counterparts in the United Kingdom.

While France could crack down on radical preachers in the 1990s, it was powerless to prevent the growth of jihadist websites and social media in the second half of the 2000s.

Jihad in Syria has become a "cause celebre" for French extremists able to access this content online. While many British extremists traveled to al Qaeda's safe havens in Afghanistan and Pakistan in the years before and after 9/11 because of their language and kinship ties to the region, much of France's banlieu population hails from North Africa, making travel to jihadist battlegrounds in the Arab world easier and more attractive.

In the wake of the attacks in Tours and Dijon, French authorities are worried about copycats in the weeks ahead.

A number of pro-ISIS extremists praised the attacks on social media, with one French radical from the banlieus now claiming to be in Syria tweeting he hoped they would be "the first of many."