Three men and a girl of 16 have been arrested with bomb-making materials by anti-terrorist police in the southern French city of Montpellier.
Home-made explosives similar to those used in the Paris attacks of November 2015 were discovered, police and judicial sources said.
Reports suggest the girl had made jihadist declarations online.
Since the beginning of 2015, at least 230 people have been killed in jihadist attacks in France.
Last month, a soldier received minor injuries when a machete-wielding man tried to enter the Louvre museum in Paris.
The man, a 29-year-old Egyptian named as Abdullah Hamamy, was shot and critically injured.
‘Allegiance to IS’
Early reports suggested that one of the Montpellier detainees was a would-be suicide attacker.
The four arrested are suspected of plotting an imminent attack, Reuters news agency quoted the interior ministry as saying.
A local news site, M6 Info, said they were planning to attack a tourist site in Paris.
They were arrested after buying acetone, a police source told AFP news agency. Acetone is an ingredient used in the making of triacetone triperoxide (TATP), a high explosive.
TATP, the same explosive used in bomb vests worn by militants in the Paris attacks, was found in the city along with the acetone, a judicial source said.
According to AFP, the female suspect had been spotted on social networks saying she wanted to leave for the Syria-Iraq conflict zone or mount an attack in France instead.
She recorded a video in which she pledged allegiance to so-called Islamic State (IS), M6 Info reports.
Meanwhile, the country’s top constitutional court struck down a law which penalised those who consult jihadist websites.
The Constitutional Council found that the law infringed on people’s freedom of communication unnecessarily.