The suspects were brought before an anti-terror judge Friday and charged with “participation in a criminal terrorist conspiracy”, the source said.
They were among 10 people detained on Tuesday in France and Switzerland after exchanging “extremely violent remarks” on the encrypted messaging app Telegram, French prosecutor Francois Molins said.
Nine of the suspects were detained in France, while the tenth, a 23-year-old Colombian woman, was held in Switzerland.
Those held in France included a 27-year-old Swiss man described as a self-styled imam tasked with indoctrination, as well as a 65-year-old army veteran and convert to Islam, and two brothers already on an extremist watchlist.
The so-called imam was in touch with a 13-year-old French teenager accused of planning a jihadist knife attack.
The minor, who was arrested in June, was the youngest person to face prosecution in France for planning a terror attack.
Molins on Friday told France Info radio the group had “corresponded on encrypted networks”.
He said they had been planning “to go into action within the (coming) months in France…”
Some of the suspects had described themselves as supporters of the Islamic State jihadist group, a judicial source said.
The French-Swiss operation came less than a week after President Emmanuel Macron signed an anti-terror law giving authorities permanent powers to search homes, shut down places of worship and restrict the movements of suspected extremists.
The new law replaced the state of emergency imposed after the November 13th, 2015 Paris attacks, which left 130 people dead.