At least 18 people have been arrested after a wave of bomb threats prompted evacuations across France.
The Palace of Versailles, the Louvre as well as schools, airports and hospitals have been targeted.
Those behind the disruption are mostly minors, authorities say.
The threats come at a time of heightened tension in France, after a teacher was fatally stabbed by an alleged jihadist last week at a school in the northern city of Arras.
Bomb scares have led to the Palace of Versailles being evacuated four times this week, while the Louvre in Paris was also forced to evacuate thousands of visitors last Saturday.
A number of regional airports were evacuated on Wednesday, including Lille, Nantes, Nice and Toulouse, and 11 airports were also affected on Thursday.
France was placed on its highest state of counter-terrorism alert last week following the killing of 57-year-old teacher Dominique Bernard. The suspect, a former pupil, is a Russian national of Chechen origin.
Schools have also been targeted by bomb scares. Six high schools in the Toulouse area alone were evacuated on Thursday and earlier this week pupils in one Toulouse school were told to go under their tables when a suspect package was spotted in front of the building.
Interior Minister Gérald Darmanin said on Thursday night that 18 people, mainly minors, had been arrested in a space of 48 hours but he stressed that France was under no specific threat.
The bomb scares have been made by phone or email, via a website launched in 2020 to text police officers direct, and by contacting official police social media accounts.
Justice Minister Éric Dupond-Moretti warned those he called “little jokers” that they would be “found and punished”.
Authorities are using IP addresses and phone numbers to identify those responsible. Calling in a fake bomb threat is a crime in France that carries up to three years in prison and a €45,000 (£39,000) fine.
