"In response to the claim of responsibility for the attack by the Islamic State and the threats against our country, we have decided to raise the Vigipirate level to its highest level: terror emergency," French Prime Minister Gabriel Attal wrote on his X account.

The decision was taken after a meeting of the French Security Council chaired by Head of State Emmanuel Macron at the Elysee Palace, four months before the start of the Olympic Games in Paris from 26 July to 11 August.

The meeting was dedicated to "the Moscow attack and its consequences", with soldiers being mobilised across the country and surveillance in public places and at borders being stepped up.

France's terror alert system has three levels, the highest of which is activated after an attack in France or abroad or when a threat is deemed imminent. It allows for exceptional security measures such as increased military patrols in public places like train stations, airports and places of worship.

In recent years, France has been the victim of several attacks claimed by jihadist groups. The most notorious were the attacks of 13 November 2015 on various leisure venues in Paris and its suburbs, in particular the Bataclan concert hall.

These events are in some ways reminiscent of last Friday's attack on the Crocus City Hall on the outskirts of Moscow. Terrorists shot dead 137 people who were attending a rock concert.

"The Moscow attack was claimed by the Islamic State-Khorasan. This organisation threatens France and has recently been involved in several foiled attacks in various European countries, including Germany and France," the prime minister's office said.

The alert level was lowered to category two (heightened security or risk of attack) in January. This is not the first time that the French national security situation has reached this level of seriousness. The highest level of alert was declared after the knife attack in the city of Arras on 13 October, which ended with the murder of Dominique Bernard.

The theft of a computer and several USB drives containing classified information on security plans for the Olympic Games was reported by a Paris City Hall employee at the end of February. In this case, the thief was arrested a few days later. Paris City Hall denied that the briefcase stolen from one of its engineers on a Paris train contained security plans for the Olympic Games.

Security is a particularly sensitive issue in France just four months before the start of the Paris Olympics. The Games are under threat from terrorism. Interior Minister Gérald Darmanin confirmed that only 326,000 tickets would be sold or distributed for the opening ceremony of the 33rd modern Olympic Games, which will be held for the first time outside an enclosed stadium on the Seine in Paris.

Organisers confirmed that their plans for the Floating Parade had been scaled back from the one million people they had previously expected to a more reasonable figure. Opposition from the French security services, common sense and the fear of terrorist attacks have prevailed over grandiose plans.

The French capital is preparing for one of the biggest security challenges in its history: 600,000 people are expected to attend the unprecedented Opening Ceremony on the Seine and an average of 40,000 security personnel will be on duty every day. The IOC has full confidence in the "plans in place."