Four people, including a 16-year-old girl, have been held by French police after bomb-making materials were found at the home of one of the suspects near Montpellier in southern France.
French Interior Minister Bruno Leroux said the police had foiled an "imminent terror plot".
A police source told AFP that four suspects aged 16, 20, 26, and 33 were arrested after they bought acetone which could be used to make an explosive device.
The prosecutor's office said that police had infiltrated the property of the 20-year-old and found acetone and 70 grams of triacetone triperoxide (TATP), the same explosive used by Islamic State (Isis/Daesh) in the 2015 Paris attacks.
The girl said on social media that she wanted to take part in the Syria-Iraq conflict or plot an attack in France, according to AFP. She reportedly posted a video pledging her allegiance to IS on 8 February.
She was planning to travel to Syria with a fake passport, according to BFM TV channel. Her boyfriend, 20, was suspected of plotting a suicide attack on a tourist attraction in Paris.
French Prime Minister Bernard Cazeneuve warned that the "terror threat in France is very high". The country has been on a high terror alert since the 2015 Paris attacks. A state of emergency was declared in July after a terrorist drove a 19-tonne truck through the centre of Nice, killing 86 people. On 3 February a man wielding a machete was shot outside the Louvre by a French soldier.