France has repeatedly been hit by deadly Islamic State attacks, including the Bataclan theatre massacre in 2015 in which extremists opened fire on concert-goers and held hostages for hours.
French troops have also fought against Islamic extremists in the Middle East and Africa.
France was already on high-security alert ahead of the Paris Olympics and Paralympics this year, which are expected to draw millions of visitors to the country.
Security concerns are notably high for the exceptional opening ceremony July 26, which will involve boats riding along the Seine River and huge crowds watching from the embankments.
