The government raised the country's terror threat level to its maximum on Sunday as France is a frequent target of the Islamic State (IS) group, which has claimed responsibility for Friday's bloodshed in the Russian capital.

President Emmanuel Macron said on Monday that the IS unit, known as Khorasan, which is a branch in Afghanistan and Pakistan, believed to be behind the killings, had also tried to attack France.

"This particular group has made several attempts (to carry out attacks) on our own soil," Macron told reporters after arriving for a trip to the French South American region of French Guiana. Interior Minister Gerald Darmanin said that the Paris Olympics, which begin on 26 July, were an obvious future target. 

"France, because we defend universal values, and are in favour of secularism... is particularly threatened, especially during extraordinary events like the Olympic Games," he told reporters.

"The French police, the gendarmes, the prefects, the intelligence services, will be ready. We have a very effective intelligence system and we are stopping plots developing almost every month," he insisted. 

The heads of intelligence services would hold a meeting on Thursday "to discuss all the conclusions of the attack on Moscow," he added. French Prime Minister Gabriel Attal said that 4,000 extra soldiers would be deployed across the country in the coming days. "The terrorist threat is real, it's strong," he told reporters, adding that two plots had already been foiled this year.

The Olympics have been attacked in the past, most infamously in Munich in 1972 and again in Atlanta in 1996, with the thousands of athletes, huge crowds and live global television audience making them a target. French organisers have faced persistent questions over their choice of opening ceremony, which will be held outside of the athletics stadium for the first time.

Instaed, the athletes will sail down the Seine in a flotilla of river boats in a made-for-TV extravaganza that has been opposed by some security officials because of the challenges it poses for police. Organisers say there is no plan B, but have hinted that the ceremony could be downgraded - meaning the athletes could not board the boats - if there are credible threats against the event..

"Our fight against terrorism is not just about words. It is very concrete and our hand will never tremble in the face of terrorism, never in the face of Islamism," Attal added. French security forces are screening up to one million people ahead of the Games, including athletes and people living near key infrastructure, according to the interior ministry.

Attal said 45 terrorist attacks had been foiled in France since 2017. The two incidents this year involved a 22-year-old suspected of planning to attack a nightclub or the LGBT or Jewish communities, and a 62-year-old suspected jihadist who wanted to target the Catholic Church, the prosecutor's office said in a statement.