The eight, all male and aged between 17 and 29, have been charged with "criminal terrorist conspiracy" in association with Logan Alexandre Nisin, a 21-year-old far-right activist who was arrested near Marseille in June.
Six of them have been placed in pre-trial detention, another was detained awaiting a further hearing on his situation and one teenager was placed under judicial control.
The prosecutor's office in Paris said that the group formed by Nisin "had plans to commit violent actions" but said the details were vague.
Targeted politicians, racial minorities, mosques
Potential targets included government spokesman Christophe Castaner, who used to be a mayor near where Nisin lived, hard-left leader Jean-Luc Mélenchon, mosques, members of racial minorities and anti-fascist activists.
Police rounded up 10 people in the Paris region and south-east France in relation to the alleged plot on Tuesday.
Two of them, including Nisin's mother, have been released.
The investigation found that the group planned to buy weapons and organise paramilitary training exercises and that some of them had already carried out shooting practice, accoding to sources.
They also intended to extort money to that end from business owners.
Nisin is suspected of involvement in the theft in a vehicle in June and two of the suspects have been charged with "theft in relation with a terrorist plot".
Royalists disown Nisin
The far-right, royalist group Action Française on Thursday complained that reports of the case had associated it with Nisin, who was a member from the end of 2015 until June 2016, claiming that he was a "lone wolf" who had become "radicalised" after leaving its ranks.
Also on Thursday, Interior Minister Christophe Collomb played down concerns that neither Castaner nor Mélenchon knew about the alleged threat to their persons, leading Mélenchon's supporters to complain that a request for security during the parliamentary election campaign had been turned down.
"Believe me there were people of the DGSI [intelligence service] who had to follow [Mélenchon] so as to protect him," Collomb told France Info radio, without spelling out whether the left-winger knew this was the case.
And, in any case, "it wasn't the most serious gang that has been stopped in recent times", he added.
France is on high security alert, although most of the authorities' attention is directed towards potential Islamist terror
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