France is once again the victim of an unspeakably cruel terror attack, in which at least 84 people were killed, including children, and at least 50 critically injured, after a truck drove through a crowd celebrating Bastille Day in Nice on Thursday evening.

The driver of the truck, a 31-year-old man of French-Tunisian origin, ploughed on for two kilometres, trying to mow down as many people as possible, before being shot dead by police. The vehicle was full of weapons and grenades, which means that far more people could have been killed had the police not neutralised the terrorist.

Isis yesterday claimed responsibility for the attack. French President François Hollande has extended a state of emergency by a further three months, saying: “All of France is under the threat of Islamic terrorism.”

The French can be forgiven for feeling they are under siege. Last month a man claiming allegiance to Isis killed two police officers in Magnanville, near Paris.

That act of terror was preceded by November’s multiple attacks in which seven gunmen and suicide bombers slaughtered 130 people in the capital. Earlier attacks included a decapitation in Lyon by a man with suspected links to Islamists, the Charlie Hebdo atrocity that left 17 dead and the March 2012 murder of seven people in Toulouse and Montauban, including a teacher and three children at a Jewish school.

France seems to be more at risk from jihadist terrorism than other European countries for a number of reasons. It is playing a major role in the fight against Islamist extremism in the Maghreb, as well as against Isis in Syria and Iraq, where it has joined the US-led airstrikes. It is also home to nearly five million Muslims, a small minority of whom are not well integrated into society and are easily radicalised. Of these, some go to Syria and return to France with military experience.

There are no easy solutions to curb this cycle of terrorism. What is needed is a combination of intelligence, security, social, military and political measures. President Hollande has said that “operational reserves” would be deployed to support the army and security forces, with a particular focus on the borders. This is fine but it will obviously take more than that to get to the root of the problem.

The authorities and the leaders of the Muslim community in France must acknowledge that radical Islam is a problem and that everything must be done to stamp it out. Muslim leaders must make it clear that violence is absolutely unacceptable while the French government must intensify its efforts to promote the integration of Muslims into French society. Centres of radicalisation must be closed down and penalties for encouraging jihadism increased.

Security, surveillance and intelligence gathering in France must be intensified and revised. The Nice killer had been in trouble with the police in the past for petty crime but he was not on the watch list of radicalised young men, so it is not yet clear whether this was an intelligence failure.

It is also true that if we want to live in a free society then no security infrastructure can be 100 per cent perfect. One may be justified, however, in asking whether the French authorities are doing everything possible to prevent atrocities like this. For example, the erection of special barriers and bollards could have stopped a truck from making it through to the large crowds celebrating Bastille Day on the main boulevard in Nice.

France, whose democratic values have been an inspiration to the entire world, needs the help and solidarity of its European partners at this delicate period.

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