French security agents have arrested six people on suspicion of plotting to attack President Emmanuel Macron, according to a judicial official.
Prosecutors have opened a preliminary investigation of alleged criminal terrorist association, the official said.
Intelligence agents detained the six suspects in three scattered regions: one in the Alps, another in Brittany and four near the Belgian border in Moselle, the official added.
The alleged plan to target the French president appeared to be vague and unfinished but violent, the official said.
Authorities said the six were aged between 22 and 62 and included one woman.
Interior minister Christophe Castaner told reporters they are believed to be far-right activists.
Authorities feared “concrete threats” from the group, Mr Castaner said.
French presidents have been targeted several times over the decades.
In 2002, a far-right sympathiser tried to attack Jacques Chirac on the Champs-Elysees Avenue in Paris during Bastille Day celebrations.
Mr Macron was in the north-eastern French city of Verdun on Tuesday as part of centenary commemorations for the end of the First World War.
The alleged plot was uncovered days before US President Donald Trump and dozens of other world leaders are due in France for weekend observances marking the signing 100 years ago of the November 11 armistice that ended the First World War.